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[ceph.git] / ceph / src / civetweb / src / third_party / duktape-1.8.0 / src-separate / duk_debugger.c

/*
 *  Duktape debugger
 */

#include "duk_internal.h"

#if defined(DUK_USE_DEBUGGER_SUPPORT)

/*
 *  Helper structs
 */

typedef union {
        void *p;
        duk_uint_t b[1];
        /* Use b[] to access the size of the union, which is strictly not
         * correct.  Can't use fixed size unless there's feature detection
         * for pointer byte size.
         */
} duk__ptr_union;

/*
 *  Detach handling
 */

#define DUK__SET_CONN_BROKEN(thr,reason) do { \
                /* For now shared handler is fine. */ \
                duk__debug_do_detach1((thr)->heap, (reason)); \
        } while (0)

DUK_LOCAL void duk__debug_do_detach1(duk_heap *heap, duk_int_t reason) {
        /* Can be called multiple times with no harm.  Mark the transport
         * bad (dbg_read_cb == NULL) and clear state except for the detached
         * callback and the udata field.  The detached callback is delayed
         * to the message loop so that it can be called between messages;
         * this avoids corner cases related to immediate debugger reattach
         * inside the detached callback.
         */

        if (heap->dbg_detaching) {
                DUK_D(DUK_DPRINT("debugger already detaching, ignore detach1"));
                return;
        }

        DUK_D(DUK_DPRINT("debugger transport detaching, marking transport broken"));

        heap->dbg_detaching = 1;  /* prevent multiple in-progress detaches */

        if (heap->dbg_write_cb != NULL) {
                duk_hthread *thr;

                thr = heap->heap_thread;
                DUK_ASSERT(thr != NULL);

                duk_debug_write_notify(thr, DUK_DBG_CMD_DETACHING);
                duk_debug_write_int(thr, reason);
                duk_debug_write_eom(thr);
        }

        heap->dbg_read_cb = NULL;
        heap->dbg_write_cb = NULL;
        heap->dbg_peek_cb = NULL;
        heap->dbg_read_flush_cb = NULL;
        heap->dbg_write_flush_cb = NULL;
        heap->dbg_request_cb = NULL;
        /* heap->dbg_detached_cb: keep */
        /* heap->dbg_udata: keep */
        /* heap->dbg_processing: keep on purpose to avoid debugger re-entry in detaching state */
        heap->dbg_paused = 0;
        heap->dbg_state_dirty = 0;
        heap->dbg_force_restart = 0;
        heap->dbg_step_type = 0;
        heap->dbg_step_thread = NULL;
        heap->dbg_step_csindex = 0;
        heap->dbg_step_startline = 0;
        heap->dbg_have_next_byte = 0;

        /* Ensure there are no stale active breakpoint pointers.
         * Breakpoint list is currently kept - we could empty it
         * here but we'd need to handle refcounts correctly, and
         * we'd need a 'thr' reference for that.
         *
         * XXX: clear breakpoint on either attach or detach?
         */
        heap->dbg_breakpoints_active[0] = (duk_breakpoint *) NULL;
}

DUK_LOCAL void duk__debug_do_detach2(duk_heap *heap) {
        duk_debug_detached_function detached_cb;
        void *detached_udata;

        /* Safe to call multiple times. */

        detached_cb = heap->dbg_detached_cb;
        detached_udata = heap->dbg_udata;
        heap->dbg_detached_cb = NULL;
        heap->dbg_udata = NULL;

        if (detached_cb) {
                /* Careful here: state must be wiped before the call
                 * so that we can cleanly handle a re-attach from
                 * inside the callback.
                 */
                DUK_D(DUK_DPRINT("detached during message loop, delayed call to detached_cb"));
                detached_cb(detached_udata);
        }

        heap->dbg_detaching = 0;
}

DUK_INTERNAL void duk_debug_do_detach(duk_heap *heap) {
        duk__debug_do_detach1(heap, 0);
        duk__debug_do_detach2(heap);
}

/* Called on a read/write error: NULL all callbacks except the detached
 * callback so that we never accidentally call them after a read/write
 * error has been indicated.  This is especially important for the transport
 * I/O callbacks to fulfill guaranteed callback semantics.
 */
DUK_LOCAL void duk__debug_null_most_callbacks(duk_hthread *thr) {
        duk_heap *heap;
        heap = thr->heap;
        DUK_D(DUK_DPRINT("transport read/write error, NULL all callbacks expected detached"));
        heap->dbg_read_cb = NULL;
        heap->dbg_write_cb = NULL;  /* this is especially critical to avoid another write call in detach1() */
        heap->dbg_peek_cb = NULL;
        heap->dbg_read_flush_cb = NULL;
        heap->dbg_write_flush_cb = NULL;
        heap->dbg_request_cb = NULL;
        /* keep heap->dbg_detached_cb */
}

/*
 *  Debug connection peek and flush primitives
 */

DUK_INTERNAL duk_bool_t duk_debug_read_peek(duk_hthread *thr) {
        duk_heap *heap;

        DUK_ASSERT(thr != NULL);
        heap = thr->heap;
        DUK_ASSERT(heap != NULL);

        if (heap->dbg_read_cb == NULL) {
                DUK_D(DUK_DPRINT("attempt to peek in detached state, return zero (= no data)"));
                return 0;
        }
        if (heap->dbg_peek_cb == NULL) {
                DUK_DD(DUK_DDPRINT("no peek callback, return zero (= no data)"));
                return 0;
        }

        return (duk_bool_t) (heap->dbg_peek_cb(heap->dbg_udata) > 0);
}

DUK_INTERNAL void duk_debug_read_flush(duk_hthread *thr) {
        duk_heap *heap;

        DUK_ASSERT(thr != NULL);
        heap = thr->heap;
        DUK_ASSERT(heap != NULL);

        if (heap->dbg_read_cb == NULL) {
                DUK_D(DUK_DPRINT("attempt to read flush in detached state, ignore"));
                return;
        }
        if (heap->dbg_read_flush_cb == NULL) {
                DUK_DD(DUK_DDPRINT("no read flush callback, ignore"));
                return;
        }

        heap->dbg_read_flush_cb(heap->dbg_udata);
}

DUK_INTERNAL void duk_debug_write_flush(duk_hthread *thr) {
        duk_heap *heap;

        DUK_ASSERT(thr != NULL);
        heap = thr->heap;
        DUK_ASSERT(heap != NULL);

        if (heap->dbg_read_cb == NULL) {
                DUK_D(DUK_DPRINT("attempt to write flush in detached state, ignore"));
                return;
        }
        if (heap->dbg_write_flush_cb == NULL) {
                DUK_DD(DUK_DDPRINT("no write flush callback, ignore"));
                return;
        }

        heap->dbg_write_flush_cb(heap->dbg_udata);
}

/*
 *  Debug connection skip primitives
 */

/* Skip fully. */
DUK_INTERNAL void duk_debug_skip_bytes(duk_hthread *thr, duk_size_t length) {
        duk_uint8_t dummy[64];
        duk_size_t now;

        DUK_ASSERT(thr != NULL);

        while (length > 0) {
                now = (length > sizeof(dummy) ? sizeof(dummy) : length);
                duk_debug_read_bytes(thr, dummy, now);
                length -= now;
        }
}

DUK_INTERNAL void duk_debug_skip_byte(duk_hthread *thr) {
        DUK_ASSERT(thr != NULL);

        (void) duk_debug_read_byte(thr);
}

/*
 *  Debug connection read primitives
 */

/* Peek ahead in the stream one byte. */
DUK_INTERNAL uint8_t duk_debug_peek_byte(duk_hthread *thr) {
        /* It is important not to call this if the last byte read was an EOM.
         * Reading ahead in this scenario would cause unnecessary blocking if
         * another message is not available.
         */

        duk_uint8_t x;

        x = duk_debug_read_byte(thr);
        thr->heap->dbg_have_next_byte = 1;
        thr->heap->dbg_next_byte = x;
        return x;
}

/* Read fully. */
DUK_INTERNAL void duk_debug_read_bytes(duk_hthread *thr, duk_uint8_t *data, duk_size_t length) {
        duk_heap *heap;
        duk_uint8_t *p;
        duk_size_t left;
        duk_size_t got;

        DUK_ASSERT(thr != NULL);
        heap = thr->heap;
        DUK_ASSERT(heap != NULL);

        if (heap->dbg_read_cb == NULL) {
                DUK_D(DUK_DPRINT("attempt to read %ld bytes in detached state, return zero data", (long) length));
                goto fail;
        }

        /* NOTE: length may be zero */
        p = data;
        if (length >= 1 && heap->dbg_have_next_byte) {
                heap->dbg_have_next_byte = 0;
                *p++ = heap->dbg_next_byte;
        }
        for (;;) {
                left = (duk_size_t) ((data + length) - p);
                if (left == 0) {
                        break;
                }
                DUK_ASSERT(heap->dbg_read_cb != NULL);
                DUK_ASSERT(left >= 1);
#if defined(DUK_USE_DEBUGGER_TRANSPORT_TORTURE)
                left = 1;
#endif
                got = heap->dbg_read_cb(heap->dbg_udata, (char *) p, left);
                if (got == 0 || got > left) {
                        DUK_D(DUK_DPRINT("connection error during read, return zero data"));
                        duk__debug_null_most_callbacks(thr);  /* avoid calling write callback in detach1() */
                        DUK__SET_CONN_BROKEN(thr, 1);
                        goto fail;
                }
                p += got;
        }
        return;

 fail:
        DUK_MEMZERO((void *) data, (size_t) length);
}

DUK_INTERNAL duk_uint8_t duk_debug_read_byte(duk_hthread *thr) {
        duk_uint8_t x;

        x = 0;  /* just in case callback is broken and won't write 'x' */
        duk_debug_read_bytes(thr, &x, 1);
        return x;
}

DUK_LOCAL duk_uint32_t duk__debug_read_uint32_raw(duk_hthread *thr) {
        duk_uint8_t buf[4];

        DUK_ASSERT(thr != NULL);

        duk_debug_read_bytes(thr, buf, 4);
        return ((duk_uint32_t) buf[0] << 24) |
               ((duk_uint32_t) buf[1] << 16) |
               ((duk_uint32_t) buf[2] << 8) |
               (duk_uint32_t) buf[3];
}

DUK_LOCAL duk_uint32_t duk__debug_read_int32_raw(duk_hthread *thr) {
        return (duk_int32_t) duk__debug_read_uint32_raw(thr);
}

DUK_LOCAL duk_uint16_t duk__debug_read_uint16_raw(duk_hthread *thr) {
        duk_uint8_t buf[2];

        DUK_ASSERT(thr != NULL);

        duk_debug_read_bytes(thr, buf, 2);
        return ((duk_uint16_t) buf[0] << 8) |
               (duk_uint16_t) buf[1];
}

DUK_INTERNAL duk_int32_t duk_debug_read_int(duk_hthread *thr) {
        duk_small_uint_t x;
        duk_small_uint_t t;

        DUK_ASSERT(thr != NULL);

        x = duk_debug_read_byte(thr);
        if (x >= 0xc0) {
                t = duk_debug_read_byte(thr);
                return (duk_int32_t) (((x - 0xc0) << 8) + t);
        } else if (x >= 0x80) {
                return (duk_int32_t) (x - 0x80);
        } else if (x == DUK_DBG_IB_INT4) {
                return (duk_int32_t) duk__debug_read_uint32_raw(thr);
        }

        DUK_D(DUK_DPRINT("debug connection error: failed to decode int"));
        DUK__SET_CONN_BROKEN(thr, 1);
        return 0;
}

DUK_LOCAL duk_hstring *duk__debug_read_hstring_raw(duk_hthread *thr, duk_uint32_t len) {
        duk_context *ctx = (duk_context *) thr;
        duk_uint8_t buf[31];
        duk_uint8_t *p;

        if (len <= sizeof(buf)) {
                duk_debug_read_bytes(thr, buf, (duk_size_t) len);
                duk_push_lstring(ctx, (const char *) buf, (duk_size_t) len);
        } else {
                p = (duk_uint8_t *) duk_push_fixed_buffer(ctx, (duk_size_t) len);
                DUK_ASSERT(p != NULL);
                duk_debug_read_bytes(thr, p, (duk_size_t) len);
                duk_to_string(ctx, -1);
        }

        return duk_require_hstring(ctx, -1);
}

DUK_INTERNAL duk_hstring *duk_debug_read_hstring(duk_hthread *thr) {
        duk_context *ctx = (duk_context *) thr;
        duk_small_uint_t x;
        duk_uint32_t len;

        DUK_ASSERT(thr != NULL);

        x = duk_debug_read_byte(thr);
        if (x >= 0x60 && x <= 0x7f) {
                /* For short strings, use a fixed temp buffer. */
                len = (duk_uint32_t) (x - 0x60);
        } else if (x == DUK_DBG_IB_STR2) {
                len = (duk_uint32_t) duk__debug_read_uint16_raw(thr);
        } else if (x == DUK_DBG_IB_STR4) {
                len = (duk_uint32_t) duk__debug_read_uint32_raw(thr);
        } else {
                goto fail;
        }

        return duk__debug_read_hstring_raw(thr, len);

 fail:
        DUK_D(DUK_DPRINT("debug connection error: failed to decode int"));
        DUK__SET_CONN_BROKEN(thr, 1);
        duk_push_hstring_stridx(thr, DUK_STRIDX_EMPTY_STRING);  /* always push some string */
        return duk_require_hstring(ctx, -1);
}

DUK_LOCAL duk_hbuffer *duk__debug_read_hbuffer_raw(duk_hthread *thr, duk_uint32_t len) {
        duk_context *ctx = (duk_context *) thr;
        duk_uint8_t *p;

        p = (duk_uint8_t *) duk_push_fixed_buffer(ctx, (duk_size_t) len);
        DUK_ASSERT(p != NULL);
        duk_debug_read_bytes(thr, p, (duk_size_t) len);

        return duk_require_hbuffer(ctx, -1);
}

DUK_LOCAL void *duk__debug_read_pointer_raw(duk_hthread *thr) {
        duk_small_uint_t x;
        duk__ptr_union pu;

        DUK_ASSERT(thr != NULL);

        x = duk_debug_read_byte(thr);
        if (x != sizeof(pu)) {
                goto fail;
        }
        duk_debug_read_bytes(thr, (duk_uint8_t *) &pu.p, sizeof(pu));
#if defined(DUK_USE_INTEGER_LE)
        duk_byteswap_bytes((duk_uint8_t *) pu.b, sizeof(pu));
#endif
        return (void *) pu.p;

 fail:
        DUK_D(DUK_DPRINT("debug connection error: failed to decode pointer"));
        DUK__SET_CONN_BROKEN(thr, 1);
        return (void *) NULL;
}

DUK_LOCAL duk_double_t duk__debug_read_double_raw(duk_hthread *thr) {
        duk_double_union du;

        DUK_ASSERT(sizeof(du.uc) == 8);
        duk_debug_read_bytes(thr, (duk_uint8_t *) du.uc, sizeof(du.uc));
        DUK_DBLUNION_DOUBLE_NTOH(&du);
        return du.d;
}

#if 0
DUK_INTERNAL duk_heaphdr *duk_debug_read_heapptr(duk_hthread *thr) {
        duk_small_uint_t x;

        DUK_ASSERT(thr != NULL);

        x = duk_debug_read_byte(thr);
        if (x != DUK_DBG_IB_HEAPPTR) {
                goto fail;
        }

        return (duk_heaphdr *) duk__debug_read_pointer_raw(thr);

 fail:
        DUK_D(DUK_DPRINT("debug connection error: failed to decode heapptr"));
        DUK__SET_CONN_BROKEN(thr, 1);
        return NULL;
}
#endif

DUK_INTERNAL duk_heaphdr *duk_debug_read_any_ptr(duk_hthread *thr) {
        duk_small_uint_t x;

        DUK_ASSERT(thr != NULL);

        x = duk_debug_read_byte(thr);
        switch (x) {
        case DUK_DBG_IB_OBJECT:
        case DUK_DBG_IB_POINTER:
        case DUK_DBG_IB_HEAPPTR:
                /* Accept any pointer-like value; for 'object' dvalue, read
                 * and ignore the class number.
                 */
                if (x == DUK_DBG_IB_OBJECT) {
                        duk_debug_skip_byte(thr);
                }
                break;
        default:
                goto fail;
        }

        return (duk_heaphdr *) duk__debug_read_pointer_raw(thr);

 fail:
        DUK_D(DUK_DPRINT("debug connection error: failed to decode any pointer (object, pointer, heapptr)"));
        DUK__SET_CONN_BROKEN(thr, 1);
        return NULL;
}

DUK_INTERNAL duk_tval *duk_debug_read_tval(duk_hthread *thr) {
        duk_context *ctx = (duk_context *) thr;
        duk_uint8_t x;
        duk_uint_t t;
        duk_uint32_t len;

        DUK_ASSERT(thr != NULL);

        x = duk_debug_read_byte(thr);

        if (x >= 0xc0) {
                t = (duk_uint_t) (x - 0xc0);
                t = (t << 8) + duk_debug_read_byte(thr);
                duk_push_uint(ctx, (duk_uint_t) t);
                goto return_ptr;
        }
        if (x >= 0x80) {
                duk_push_uint(ctx, (duk_uint_t) (x - 0x80));
                goto return_ptr;
        }
        if (x >= 0x60) {
                len = (duk_uint32_t) (x - 0x60);
                duk__debug_read_hstring_raw(thr, len);
                goto return_ptr;
        }

        switch (x) {
        case DUK_DBG_IB_INT4: {
                duk_int32_t i = duk__debug_read_int32_raw(thr);
                duk_push_i32(ctx, i);
                break;
        }
        case DUK_DBG_IB_STR4: {
                len = duk__debug_read_uint32_raw(thr);
                duk__debug_read_hstring_raw(thr, len);
                break;
        }
        case DUK_DBG_IB_STR2: {
                len = duk__debug_read_uint16_raw(thr);
                duk__debug_read_hstring_raw(thr, len);
                break;
        }
        case DUK_DBG_IB_BUF4: {
                len = duk__debug_read_uint32_raw(thr);
                duk__debug_read_hbuffer_raw(thr, len);
                break;
        }
        case DUK_DBG_IB_BUF2: {
                len = duk__debug_read_uint16_raw(thr);
                duk__debug_read_hbuffer_raw(thr, len);
                break;
        }
        case DUK_DBG_IB_UNDEFINED: {
                duk_push_undefined(ctx);
                break;
        }
        case DUK_DBG_IB_NULL: {
                duk_push_null(ctx);
                break;
        }
        case DUK_DBG_IB_TRUE: {
                duk_push_true(ctx);
                break;
        }
        case DUK_DBG_IB_FALSE: {
                duk_push_false(ctx);
                break;
        }
        case DUK_DBG_IB_NUMBER: {
                duk_double_t d;
                d = duk__debug_read_double_raw(thr);
                duk_push_number(ctx, d);
                break;
        }
        case DUK_DBG_IB_OBJECT: {
                duk_heaphdr *h;
                duk_debug_skip_byte(thr);
                h = (duk_heaphdr *) duk__debug_read_pointer_raw(thr);
                duk_push_heapptr(thr, (void *) h);
                break;
        }
        case DUK_DBG_IB_POINTER: {
                void *ptr;
                ptr = duk__debug_read_pointer_raw(thr);
                duk_push_pointer(thr, ptr);
                break;
        }
        case DUK_DBG_IB_LIGHTFUNC: {
                /* XXX: Not needed for now, so not implemented.  Note that
                 * function pointers may have different size/layout than
                 * a void pointer.
                 */
                DUK_D(DUK_DPRINT("reading lightfunc values unimplemented"));
                goto fail;
        }
        case DUK_DBG_IB_HEAPPTR: {
                duk_heaphdr *h;
                h = (duk_heaphdr *) duk__debug_read_pointer_raw(thr);
                duk_push_heapptr(thr, (void *) h);
                break;
        }
        case DUK_DBG_IB_UNUSED:  /* unused: not accepted in inbound messages */
        default:
                goto fail;
        }

 return_ptr:
        return DUK_GET_TVAL_NEGIDX(thr, -1);

 fail:
        DUK_D(DUK_DPRINT("debug connection error: failed to decode tval"));
        DUK__SET_CONN_BROKEN(thr, 1);
        return NULL;
}

/*
 *  Debug connection write primitives
 */

/* Write fully. */
DUK_INTERNAL void duk_debug_write_bytes(duk_hthread *thr, const duk_uint8_t *data, duk_size_t length) {
        duk_heap *heap;
        const duk_uint8_t *p;
        duk_size_t left;
        duk_size_t got;

        DUK_ASSERT(thr != NULL);
        DUK_ASSERT(length == 0 || data != NULL);
        heap = thr->heap;
        DUK_ASSERT(heap != NULL);

        if (heap->dbg_write_cb == NULL) {
                DUK_D(DUK_DPRINT("attempt to write %ld bytes in detached state, ignore", (long) length));
                return;
        }
        if (length == 0) {
                /* Avoid doing an actual write callback with length == 0,
                 * because that's reserved for a write flush.
                 */
                return;
        }
        DUK_ASSERT(data != NULL);

        p = data;
        for (;;) {
                left = (duk_size_t) ((data + length) - p);
                if (left == 0) {
                        break;
                }
                DUK_ASSERT(heap->dbg_write_cb != NULL);
                DUK_ASSERT(left >= 1);
#if defined(DUK_USE_DEBUGGER_TRANSPORT_TORTURE)
                left = 1;
#endif
                got = heap->dbg_write_cb(heap->dbg_udata, (const char *) p, left);
                if (got == 0 || got > left) {
                        duk__debug_null_most_callbacks(thr);  /* avoid calling write callback in detach1() */
                        DUK_D(DUK_DPRINT("connection error during write"));
                        DUK__SET_CONN_BROKEN(thr, 1);
                        return;
                }
                p += got;
        }
}

DUK_INTERNAL void duk_debug_write_byte(duk_hthread *thr, duk_uint8_t x) {
        duk_debug_write_bytes(thr, (const duk_uint8_t *) &x, 1);
}

DUK_INTERNAL void duk_debug_write_unused(duk_hthread *thr) {
        duk_debug_write_byte(thr, DUK_DBG_IB_UNUSED);
}

DUK_INTERNAL void duk_debug_write_undefined(duk_hthread *thr) {
        duk_debug_write_byte(thr, DUK_DBG_IB_UNDEFINED);
}

#if defined(DUK_USE_DEBUGGER_INSPECT)
DUK_INTERNAL void duk_debug_write_null(duk_hthread *thr) {
        duk_debug_write_byte(thr, DUK_DBG_IB_NULL);
}
#endif

DUK_INTERNAL void duk_debug_write_boolean(duk_hthread *thr, duk_uint_t val) {
        duk_debug_write_byte(thr, val ? DUK_DBG_IB_TRUE : DUK_DBG_IB_FALSE);
}

/* Write signed 32-bit integer. */
DUK_INTERNAL void duk_debug_write_int(duk_hthread *thr, duk_int32_t x) {
        duk_uint8_t buf[5];
        duk_size_t len;

        DUK_ASSERT(thr != NULL);

        if (x >= 0 && x <= 0x3fL) {
                buf[0] = (duk_uint8_t) (0x80 + x);
                len = 1;
        } else if (x >= 0 && x <= 0x3fffL) {
                buf[0] = (duk_uint8_t) (0xc0 + (x >> 8));
                buf[1] = (duk_uint8_t) (x & 0xff);
                len = 2;
        } else {
                /* Signed integers always map to 4 bytes now. */
                buf[0] = (duk_uint8_t) DUK_DBG_IB_INT4;
                buf[1] = (duk_uint8_t) ((x >> 24) & 0xff);
                buf[2] = (duk_uint8_t) ((x >> 16) & 0xff);
                buf[3] = (duk_uint8_t) ((x >> 8) & 0xff);
                buf[4] = (duk_uint8_t) (x & 0xff);
                len = 5;
        }
        duk_debug_write_bytes(thr, buf, len);
}

/* Write unsigned 32-bit integer. */
DUK_INTERNAL void duk_debug_write_uint(duk_hthread *thr, duk_uint32_t x) {
        /* The debugger protocol doesn't support a plain integer encoding for
         * the full 32-bit unsigned range (only 32-bit signed).  For now,
         * unsigned 32-bit values simply written as signed ones.  This is not
         * a concrete issue except for 32-bit heaphdr fields.  Proper solutions
         * would be to (a) write such integers as IEEE doubles or (b) add an
         * unsigned 32-bit dvalue.
         */
        if (x >= 0x80000000UL) {
                DUK_D(DUK_DPRINT("writing unsigned integer 0x%08lx as signed integer",
                                 (long) x));
        }
        duk_debug_write_int(thr, (duk_int32_t) x);
}

DUK_INTERNAL void duk_debug_write_strbuf(duk_hthread *thr, const char *data, duk_size_t length, duk_uint8_t marker_base) {
        duk_uint8_t buf[5];
        duk_size_t buflen;

        DUK_ASSERT(thr != NULL);
        DUK_ASSERT(length == 0 || data != NULL);

        if (length <= 0x1fUL && marker_base == DUK_DBG_IB_STR4) {
                /* For strings, special form for short lengths. */
                buf[0] = (duk_uint8_t) (0x60 + length);
                buflen = 1;
        } else if (length <= 0xffffUL) {
                buf[0] = (duk_uint8_t) (marker_base + 1);
                buf[1] = (duk_uint8_t) (length >> 8);
                buf[2] = (duk_uint8_t) (length & 0xff);
                buflen = 3;
        } else {
                buf[0] = (duk_uint8_t) marker_base;
                buf[1] = (duk_uint8_t) (length >> 24);
                buf[2] = (duk_uint8_t) ((length >> 16) & 0xff);
                buf[3] = (duk_uint8_t) ((length >> 8) & 0xff);
                buf[4] = (duk_uint8_t) (length & 0xff);
                buflen = 5;
        }

        duk_debug_write_bytes(thr, (const duk_uint8_t *) buf, buflen);
        duk_debug_write_bytes(thr, (const duk_uint8_t *) data, length);
}

DUK_INTERNAL void duk_debug_write_string(duk_hthread *thr, const char *data, duk_size_t length) {
        duk_debug_write_strbuf(thr, data, length, DUK_DBG_IB_STR4);
}

DUK_INTERNAL void duk_debug_write_cstring(duk_hthread *thr, const char *data) {
        DUK_ASSERT(thr != NULL);

        duk_debug_write_string(thr,
                               data,
                               data ? DUK_STRLEN(data) : 0);
}

DUK_INTERNAL void duk_debug_write_hstring(duk_hthread *thr, duk_hstring *h) {
        DUK_ASSERT(thr != NULL);

        /* XXX: differentiate null pointer from empty string? */
        duk_debug_write_string(thr,
                               (h != NULL ? (const char *) DUK_HSTRING_GET_DATA(h) : NULL),
                               (h != NULL ? (duk_size_t) DUK_HSTRING_GET_BYTELEN(h) : 0));
}

DUK_LOCAL void duk__debug_write_hstring_safe_top(duk_hthread *thr) {
        duk_context *ctx = (duk_context *) thr;
        duk_debug_write_hstring(thr, duk_safe_to_hstring(ctx, -1));
}

DUK_INTERNAL void duk_debug_write_buffer(duk_hthread *thr, const char *data, duk_size_t length) {
        duk_debug_write_strbuf(thr, data, length, DUK_DBG_IB_BUF4);
}

DUK_INTERNAL void duk_debug_write_hbuffer(duk_hthread *thr, duk_hbuffer *h) {
        DUK_ASSERT(thr != NULL);

        duk_debug_write_buffer(thr,
                               (h != NULL ? (const char *) DUK_HBUFFER_GET_DATA_PTR(thr->heap, h) : NULL),
                               (h != NULL ? (duk_size_t) DUK_HBUFFER_GET_SIZE(h) : 0));
}

DUK_LOCAL void duk__debug_write_pointer_raw(duk_hthread *thr, void *ptr, duk_uint8_t ibyte) {
        duk_uint8_t buf[2];
        duk__ptr_union pu;

        DUK_ASSERT(thr != NULL);
        DUK_ASSERT(sizeof(ptr) >= 1 && sizeof(ptr) <= 16);
        /* ptr may be NULL */

        buf[0] = ibyte;
        buf[1] = sizeof(pu);
        duk_debug_write_bytes(thr, buf, 2);
        pu.p = (void *) ptr;
#if defined(DUK_USE_INTEGER_LE)
        duk_byteswap_bytes((duk_uint8_t *) pu.b, sizeof(pu));
#endif
        duk_debug_write_bytes(thr, (const duk_uint8_t *) &pu.p, (duk_size_t) sizeof(pu));
}

DUK_INTERNAL void duk_debug_write_pointer(duk_hthread *thr, void *ptr) {
        duk__debug_write_pointer_raw(thr, ptr, DUK_DBG_IB_POINTER);
}

#if defined(DUK_USE_DEBUGGER_DUMPHEAP) || defined(DUK_USE_DEBUGGER_INSPECT)
DUK_INTERNAL void duk_debug_write_heapptr(duk_hthread *thr, duk_heaphdr *h) {
        duk__debug_write_pointer_raw(thr, (void *) h, DUK_DBG_IB_HEAPPTR);
}
#endif  /* DUK_USE_DEBUGGER_DUMPHEAP || DUK_USE_DEBUGGER_INSPECT */

DUK_INTERNAL void duk_debug_write_hobject(duk_hthread *thr, duk_hobject *obj) {
        duk_uint8_t buf[3];
        duk__ptr_union pu;

        DUK_ASSERT(thr != NULL);
        DUK_ASSERT(sizeof(obj) >= 1 && sizeof(obj) <= 16);
        DUK_ASSERT(obj != NULL);

        buf[0] = DUK_DBG_IB_OBJECT;
        buf[1] = (duk_uint8_t) DUK_HOBJECT_GET_CLASS_NUMBER(obj);
        buf[2] = sizeof(pu);
        duk_debug_write_bytes(thr, buf, 3);
        pu.p = (void *) obj;
#if defined(DUK_USE_INTEGER_LE)
        duk_byteswap_bytes((duk_uint8_t *) pu.b, sizeof(pu));
#endif
        duk_debug_write_bytes(thr, (const duk_uint8_t *) &pu.p, (duk_size_t) sizeof(pu));
}

DUK_INTERNAL void duk_debug_write_tval(duk_hthread *thr, duk_tval *tv) {
        duk_c_function lf_func;
        duk_small_uint_t lf_flags;
        duk_uint8_t buf[4];
        duk_double_union du1;
        duk_double_union du2;
        duk_int32_t i32;

        DUK_ASSERT(thr != NULL);
        DUK_ASSERT(tv != NULL);

        switch (DUK_TVAL_GET_TAG(tv)) {
        case DUK_TAG_UNDEFINED:
                duk_debug_write_byte(thr, DUK_DBG_IB_UNDEFINED);
                break;
        case DUK_TAG_UNUSED:
                duk_debug_write_byte(thr, DUK_DBG_IB_UNUSED);
                break;
        case DUK_TAG_NULL:
                duk_debug_write_byte(thr, DUK_DBG_IB_NULL);
                break;
        case DUK_TAG_BOOLEAN:
                DUK_ASSERT(DUK_TVAL_GET_BOOLEAN(tv) == 0 ||
                           DUK_TVAL_GET_BOOLEAN(tv) == 1);
                duk_debug_write_boolean(thr, DUK_TVAL_GET_BOOLEAN(tv));
                break;
        case DUK_TAG_POINTER:
                duk_debug_write_pointer(thr, (void *) DUK_TVAL_GET_POINTER(tv));
                break;
        case DUK_TAG_LIGHTFUNC:
                DUK_TVAL_GET_LIGHTFUNC(tv, lf_func, lf_flags);
                buf[0] = DUK_DBG_IB_LIGHTFUNC;
                buf[1] = (duk_uint8_t) (lf_flags >> 8);
                buf[2] = (duk_uint8_t) (lf_flags & 0xff);
                buf[3] = sizeof(lf_func);
                duk_debug_write_bytes(thr, buf, 4);
                duk_debug_write_bytes(thr, (const duk_uint8_t *) &lf_func, sizeof(lf_func));
                break;
        case DUK_TAG_STRING:
                duk_debug_write_hstring(thr, DUK_TVAL_GET_STRING(tv));
                break;
        case DUK_TAG_OBJECT:
                duk_debug_write_hobject(thr, DUK_TVAL_GET_OBJECT(tv));
                break;
        case DUK_TAG_BUFFER:
                duk_debug_write_hbuffer(thr, DUK_TVAL_GET_BUFFER(tv));
                break;
#if defined(DUK_USE_FASTINT)
        case DUK_TAG_FASTINT:
#endif
        default:
                /* Numbers are normalized to big (network) endian.  We can
                 * (but are not required) to use integer dvalues when there's
                 * no loss of precision.
                 *
                 * XXX: share check with other code; this check is slow but
                 * reliable and doesn't require careful exponent/mantissa
                 * mask tricks as in the fastint downgrade code.
                 */
                DUK_ASSERT(!DUK_TVAL_IS_UNUSED(tv));
                DUK_ASSERT(DUK_TVAL_IS_NUMBER(tv));
                du1.d = DUK_TVAL_GET_NUMBER(tv);
                i32 = (duk_int32_t) du1.d;
                du2.d = (duk_double_t) i32;

                DUK_DD(DUK_DDPRINT("i32=%ld du1=%02x%02x%02x%02x%02x%02x%02x%02x "
                                   "du2=%02x%02x%02x%02x%02x%02x%02x%02x",
                                   (long) i32,
                                   (unsigned int) du1.uc[0], (unsigned int) du1.uc[1],
                                   (unsigned int) du1.uc[2], (unsigned int) du1.uc[3],
                                   (unsigned int) du1.uc[4], (unsigned int) du1.uc[5],
                                   (unsigned int) du1.uc[6], (unsigned int) du1.uc[7],
                                   (unsigned int) du2.uc[0], (unsigned int) du2.uc[1],
                                   (unsigned int) du2.uc[2], (unsigned int) du2.uc[3],
                                   (unsigned int) du2.uc[4], (unsigned int) du2.uc[5],
                                   (unsigned int) du2.uc[6], (unsigned int) du2.uc[7]));

                if (DUK_MEMCMP((const void *) du1.uc, (const void *) du2.uc, sizeof(du1.uc)) == 0) {
                        duk_debug_write_int(thr, i32);
                } else {
                        DUK_DBLUNION_DOUBLE_HTON(&du1);
                        duk_debug_write_byte(thr, DUK_DBG_IB_NUMBER);
                        duk_debug_write_bytes(thr, (const duk_uint8_t *) du1.uc, sizeof(du1.uc));
                }
        }
}

#if defined(DUK_USE_DEBUGGER_DUMPHEAP)
/* Variant for writing duk_tvals so that any heap allocated values are
 * written out as tagged heap pointers.
 */
DUK_LOCAL void duk__debug_write_tval_heapptr(duk_hthread *thr, duk_tval *tv) {
        if (DUK_TVAL_IS_HEAP_ALLOCATED(tv)) {
                duk_heaphdr *h = DUK_TVAL_GET_HEAPHDR(tv);
                duk_debug_write_heapptr(thr, h);
        } else {
                duk_debug_write_tval(thr, tv);
        }
}
#endif  /* DUK_USE_DEBUGGER_DUMPHEAP */

/*
 *  Debug connection message write helpers
 */

#if 0  /* unused */
DUK_INTERNAL void duk_debug_write_request(duk_hthread *thr, duk_small_uint_t command) {
        duk_debug_write_byte(thr, DUK_DBG_IB_REQUEST);
        duk_debug_write_int(thr, command);
}
#endif

DUK_INTERNAL void duk_debug_write_reply(duk_hthread *thr) {
        duk_debug_write_byte(thr, DUK_DBG_IB_REPLY);
}

DUK_INTERNAL void duk_debug_write_error_eom(duk_hthread *thr, duk_small_uint_t err_code, const char *msg) {
        /* Allow NULL 'msg' */
        duk_debug_write_byte(thr, DUK_DBG_IB_ERROR);
        duk_debug_write_int(thr, (duk_int32_t) err_code);
        duk_debug_write_cstring(thr, msg);
        duk_debug_write_eom(thr);
}

DUK_INTERNAL void duk_debug_write_notify(duk_hthread *thr, duk_small_uint_t command) {
        duk_debug_write_byte(thr, DUK_DBG_IB_NOTIFY);
        duk_debug_write_int(thr, command);
}

DUK_INTERNAL void duk_debug_write_eom(duk_hthread *thr) {
        duk_debug_write_byte(thr, DUK_DBG_IB_EOM);

        /* As an initial implementation, write flush after every EOM (and the
         * version identifier).  A better implementation would flush only when
         * Duktape is finished processing messages so that a flush only happens
         * after all outbound messages are finished on that occasion.
         */
        duk_debug_write_flush(thr);
}

/*
 *  Status message and helpers
 */

DUK_INTERNAL duk_uint_fast32_t duk_debug_curr_line(duk_hthread *thr) {
        duk_context *ctx = (duk_context *) thr;
        duk_activation *act;
        duk_uint_fast32_t line;
        duk_uint_fast32_t pc;

        act = duk_hthread_get_current_activation(thr);  /* may be NULL */
        if (act == NULL) {
                return 0;
        }

        /* We're conceptually between two opcodes; act->pc indicates the next
         * instruction to be executed.  This is usually the correct pc/line to
         * indicate in Status.  (For the 'debugger' statement this now reports
         * the pc/line after the debugger statement because the debugger opcode
         * has already been executed.)
         */

        pc = duk_hthread_get_act_curr_pc(thr, act);

        /* XXX: this should be optimized to be a raw query and avoid valstack
         * operations if possible.
         */
        duk_push_tval(ctx, &act->tv_func);
        line = duk_hobject_pc2line_query(ctx, -1, pc);
        duk_pop(ctx);
        return line;
}

DUK_INTERNAL void duk_debug_send_status(duk_hthread *thr) {
        duk_context *ctx = (duk_context *) thr;
        duk_activation *act;

        duk_debug_write_notify(thr, DUK_DBG_CMD_STATUS);
        duk_debug_write_int(thr, thr->heap->dbg_paused);

        DUK_ASSERT_DISABLE(thr->callstack_top >= 0);  /* unsigned */
        if (thr->callstack_top == 0) {
                duk_debug_write_undefined(thr);
                duk_debug_write_undefined(thr);
                duk_debug_write_int(thr, 0);
                duk_debug_write_int(thr, 0);
        } else {
                act = thr->callstack + thr->callstack_top - 1;
                duk_push_tval(ctx, &act->tv_func);
                duk_get_prop_string(ctx, -1, "fileName");
                duk__debug_write_hstring_safe_top(thr);
                duk_get_prop_string(ctx, -2, "name");
                duk__debug_write_hstring_safe_top(thr);
                duk_pop_3(ctx);
                /* Report next pc/line to be executed. */
                duk_debug_write_uint(thr, (duk_uint32_t) duk_debug_curr_line(thr));
                act = thr->callstack + thr->callstack_top - 1;
                duk_debug_write_uint(thr, (duk_uint32_t) duk_hthread_get_act_curr_pc(thr, act));
        }

        duk_debug_write_eom(thr);
}

#if defined(DUK_USE_DEBUGGER_THROW_NOTIFY)
DUK_INTERNAL void duk_debug_send_throw(duk_hthread *thr, duk_bool_t fatal) {
        /*
         *  NFY <int: 5> <int: fatal> <str: msg> <str: filename> <int: linenumber> EOM
         */

        duk_context *ctx = (duk_context *) thr;
        duk_activation *act;
        duk_uint32_t pc;

        DUK_ASSERT(thr->valstack_top > thr->valstack);  /* At least: ... [err] */

        duk_debug_write_notify(thr, DUK_DBG_CMD_THROW);
        duk_debug_write_int(thr, fatal);

        /* Report thrown value to client coerced to string */
        duk_dup(ctx, -1);
        duk__debug_write_hstring_safe_top(thr);
        duk_pop(ctx);

        if (duk_is_error(ctx, -1)) {
                /* Error instance, use augmented error data directly */
                duk_get_prop_stridx(ctx, -1, DUK_STRIDX_FILE_NAME);
                duk__debug_write_hstring_safe_top(thr);
                duk_get_prop_stridx(ctx, -2, DUK_STRIDX_LINE_NUMBER);
                duk_debug_write_uint(thr, duk_get_uint(ctx, -1));
                duk_pop_2(ctx);
        } else {
                /* For anything other than an Error instance, we calculate the
                 * error location directly from the current activation if one
                 * exists.
                 */
                if (thr->callstack_top > 0) {
                        act = thr->callstack + thr->callstack_top - 1;
                        duk_push_tval(ctx, &act->tv_func);
                        duk_get_prop_string(ctx, -1, "fileName");
                        duk__debug_write_hstring_safe_top(thr);
                        act = thr->callstack + thr->callstack_top - 1;
                        pc = duk_hthread_get_act_prev_pc(thr, act);
                        duk_debug_write_uint(thr, (duk_uint32_t) duk_hobject_pc2line_query(ctx, -2, pc));
                        duk_pop_2(ctx);
                } else {
                        /* Can happen if duk_throw() is called on an empty
                         * callstack.
                         */
                        duk_debug_write_cstring(thr, "");
                        duk_debug_write_uint(thr, 0);
                }
        }

        duk_debug_write_eom(thr);
}
#endif  /* DUK_USE_DEBUGGER_THROW_NOTIFY */

/*
 *  Debug message processing
 */

/* Skip dvalue. */
DUK_LOCAL duk_bool_t duk__debug_skip_dvalue(duk_hthread *thr) {
        duk_uint8_t x;
        duk_uint32_t len;

        x = duk_debug_read_byte(thr);

        if (x >= 0xc0) {
                duk_debug_skip_byte(thr);
                return 0;
        }
        if (x >= 0x80) {
                return 0;
        }
        if (x >= 0x60) {
                duk_debug_skip_bytes(thr, x - 0x60);
                return 0;
        }
        switch(x) {
        case DUK_DBG_IB_EOM:
                return 1;  /* Return 1: got EOM */
        case DUK_DBG_IB_REQUEST:
        case DUK_DBG_IB_REPLY:
        case DUK_DBG_IB_ERROR:
        case DUK_DBG_IB_NOTIFY:
                break;
        case DUK_DBG_IB_INT4:
                (void) duk__debug_read_uint32_raw(thr);
                break;
        case DUK_DBG_IB_STR4:
        case DUK_DBG_IB_BUF4:
                len = duk__debug_read_uint32_raw(thr);
                duk_debug_skip_bytes(thr, len);
                break;
        case DUK_DBG_IB_STR2:
        case DUK_DBG_IB_BUF2:
                len = duk__debug_read_uint16_raw(thr);
                duk_debug_skip_bytes(thr, len);
                break;
        case DUK_DBG_IB_UNUSED:
        case DUK_DBG_IB_UNDEFINED:
        case DUK_DBG_IB_NULL:
        case DUK_DBG_IB_TRUE:
        case DUK_DBG_IB_FALSE:
                break;
        case DUK_DBG_IB_NUMBER:
                duk_debug_skip_bytes(thr, 8);
                break;
        case DUK_DBG_IB_OBJECT:
                duk_debug_skip_byte(thr);
                len = duk_debug_read_byte(thr);
                duk_debug_skip_bytes(thr, len);
                break;
        case DUK_DBG_IB_POINTER:
        case DUK_DBG_IB_HEAPPTR:
                len = duk_debug_read_byte(thr);
                duk_debug_skip_bytes(thr, len);
                break;
        case DUK_DBG_IB_LIGHTFUNC:
                duk_debug_skip_bytes(thr, 2);
                len = duk_debug_read_byte(thr);
                duk_debug_skip_bytes(thr, len);
                break;
        default:
                goto fail;
        }

        return 0;

 fail:
        DUK__SET_CONN_BROKEN(thr, 1);
        return 1;  /* Pretend like we got EOM */
}

/* Skip dvalues to EOM. */
DUK_LOCAL void duk__debug_skip_to_eom(duk_hthread *thr) {
        for (;;) {
                if (duk__debug_skip_dvalue(thr)) {
                        break;
                }
        }
}

/*
 *  Simple commands
 */

DUK_LOCAL void duk__debug_handle_basic_info(duk_hthread *thr, duk_heap *heap) {
        DUK_UNREF(heap);
        DUK_D(DUK_DPRINT("debug command Version"));

        duk_debug_write_reply(thr);
        duk_debug_write_int(thr, DUK_VERSION);
        duk_debug_write_cstring(thr, DUK_GIT_DESCRIBE);
        duk_debug_write_cstring(thr, DUK_USE_TARGET_INFO);
#if defined(DUK_USE_DOUBLE_LE)
        duk_debug_write_int(thr, 1);
#elif defined(DUK_USE_DOUBLE_ME)
        duk_debug_write_int(thr, 2);
#elif defined(DUK_USE_DOUBLE_BE)
        duk_debug_write_int(thr, 3);
#else
        duk_debug_write_int(thr, 0);
#endif
        duk_debug_write_int(thr, (duk_int_t) sizeof(void *));
        duk_debug_write_eom(thr);
}

DUK_LOCAL void duk__debug_handle_trigger_status(duk_hthread *thr, duk_heap *heap) {
        DUK_UNREF(heap);
        DUK_D(DUK_DPRINT("debug command TriggerStatus"));

        duk_debug_write_reply(thr);
        duk_debug_write_eom(thr);
        heap->dbg_state_dirty = 1;
}

DUK_LOCAL void duk__debug_handle_pause(duk_hthread *thr, duk_heap *heap) {
        DUK_D(DUK_DPRINT("debug command Pause"));

        DUK_HEAP_SET_PAUSED(heap);
        duk_debug_write_reply(thr);
        duk_debug_write_eom(thr);
}

DUK_LOCAL void duk__debug_handle_resume(duk_hthread *thr, duk_heap *heap) {
        DUK_D(DUK_DPRINT("debug command Resume"));

        DUK_HEAP_CLEAR_PAUSED(heap);
        duk_debug_write_reply(thr);
        duk_debug_write_eom(thr);
}

DUK_LOCAL void duk__debug_handle_step(duk_hthread *thr, duk_heap *heap, duk_int32_t cmd) {
        duk_small_uint_t step_type;
        duk_uint_fast32_t line;

        DUK_D(DUK_DPRINT("debug command StepInto/StepOver/StepOut: %d", (int) cmd));

        if (cmd == DUK_DBG_CMD_STEPINTO) {
                step_type = DUK_STEP_TYPE_INTO;
        } else if (cmd == DUK_DBG_CMD_STEPOVER) {
                step_type = DUK_STEP_TYPE_OVER;
        } else {
                DUK_ASSERT(cmd == DUK_DBG_CMD_STEPOUT);
                step_type = DUK_STEP_TYPE_OUT;
        }

        line = duk_debug_curr_line(thr);
        if (line > 0) {
                heap->dbg_paused = 0;
                heap->dbg_step_type = step_type;
                heap->dbg_step_thread = thr;
                heap->dbg_step_csindex = thr->callstack_top - 1;
                heap->dbg_step_startline = line;
                heap->dbg_state_dirty = 1;
        } else {
                DUK_D(DUK_DPRINT("cannot determine current line, stepinto/stepover/stepout ignored"));
        }
        duk_debug_write_reply(thr);
        duk_debug_write_eom(thr);
}

DUK_LOCAL void duk__debug_handle_list_break(duk_hthread *thr, duk_heap *heap) {
        duk_small_int_t i;

        DUK_D(DUK_DPRINT("debug command ListBreak"));
        duk_debug_write_reply(thr);
        for (i = 0; i < (duk_small_int_t) heap->dbg_breakpoint_count; i++) {
                duk_debug_write_hstring(thr, heap->dbg_breakpoints[i].filename);
                duk_debug_write_uint(thr, (duk_uint32_t) heap->dbg_breakpoints[i].line);
        }
        duk_debug_write_eom(thr);
}

DUK_LOCAL void duk__debug_handle_add_break(duk_hthread *thr, duk_heap *heap) {
        duk_hstring *filename;
        duk_uint32_t linenumber;
        duk_small_int_t idx;

        DUK_UNREF(heap);

        filename = duk_debug_read_hstring(thr);
        linenumber = (duk_uint32_t) duk_debug_read_int(thr);
        DUK_D(DUK_DPRINT("debug command AddBreak: %!O:%ld", (duk_hobject *) filename, (long) linenumber));
        idx = duk_debug_add_breakpoint(thr, filename, linenumber);
        if (idx >= 0) {
                duk_debug_write_reply(thr);
                duk_debug_write_int(thr, (duk_int32_t) idx);
                duk_debug_write_eom(thr);
        } else {
                duk_debug_write_error_eom(thr, DUK_DBG_ERR_TOOMANY, "no space for breakpoint");
        }
}

DUK_LOCAL void duk__debug_handle_del_break(duk_hthread *thr, duk_heap *heap) {
        duk_small_uint_t idx;

        DUK_UNREF(heap);

        DUK_D(DUK_DPRINT("debug command DelBreak"));
        idx = (duk_small_uint_t) duk_debug_read_int(thr);
        if (duk_debug_remove_breakpoint(thr, idx)) {
                duk_debug_write_reply(thr);
                duk_debug_write_eom(thr);
        } else {
                duk_debug_write_error_eom(thr, DUK_DBG_ERR_NOTFOUND, "invalid breakpoint index");
        }
}

DUK_LOCAL void duk__debug_handle_get_var(duk_hthread *thr, duk_heap *heap) {
        duk_context *ctx = (duk_context *) thr;
        duk_hstring *str;
        duk_bool_t rc;
        duk_int32_t level;

        DUK_UNREF(heap);
        DUK_D(DUK_DPRINT("debug command GetVar"));

        str = duk_debug_read_hstring(thr);  /* push to stack */
        DUK_ASSERT(str != NULL);
        if (duk_debug_peek_byte(thr) != DUK_DBG_IB_EOM) {
                level = duk_debug_read_int(thr);  /* optional callstack level */
                if (level >= 0 || -level > (duk_int32_t) thr->callstack_top) {
                        DUK_D(DUK_DPRINT("invalid callstack level for GetVar"));
                        duk_debug_write_error_eom(thr, DUK_DBG_ERR_NOTFOUND, "invalid callstack level");
                        return;
                }
        } else {
                level = -1;
        }

        if (thr->callstack_top > 0) {
                rc = duk_js_getvar_activation(thr,
                                              thr->callstack + thr->callstack_top + level,
                                              str,
                                              0);
        } else {
                /* No activation, no variable access.  Could also pretend
                 * we're in the global program context and read stuff off
                 * the global object.
                 */
                DUK_D(DUK_DPRINT("callstack empty, no activation -> ignore getvar"));
                rc = 0;
        }

        duk_debug_write_reply(thr);
        if (rc) {
                duk_debug_write_int(thr, 1);
                DUK_ASSERT(duk_get_tval(ctx, -2) != NULL);
                duk_debug_write_tval(thr, duk_get_tval(ctx, -2));
        } else {
                duk_debug_write_int(thr, 0);
                duk_debug_write_unused(thr);
        }
        duk_debug_write_eom(thr);
}

DUK_LOCAL void duk__debug_handle_put_var(duk_hthread *thr, duk_heap *heap) {
        duk_hstring *str;
        duk_tval *tv;
        duk_int32_t level;

        DUK_UNREF(heap);
        DUK_D(DUK_DPRINT("debug command PutVar"));

        str = duk_debug_read_hstring(thr);  /* push to stack */
        DUK_ASSERT(str != NULL);
        tv = duk_debug_read_tval(thr);
        if (tv == NULL) {
                /* detached */
                return;
        }
        if (duk_debug_peek_byte(thr) != DUK_DBG_IB_EOM) {
                level = duk_debug_read_int(thr);  /* optional callstack level */
                if (level >= 0 || -level > (duk_int32_t) thr->callstack_top) {
                        DUK_D(DUK_DPRINT("invalid callstack level for PutVar"));
                        duk_debug_write_error_eom(thr, DUK_DBG_ERR_NOTFOUND, "invalid callstack level");
                        return;
                }
        } else {
                level = -1;
        }

        if (thr->callstack_top > 0) {
                duk_js_putvar_activation(thr,
                                         thr->callstack + thr->callstack_top + level,
                                         str,
                                         tv,
                                         0);
        } else {
                DUK_D(DUK_DPRINT("callstack empty, no activation -> ignore putvar"));
        }

        /* XXX: Current putvar implementation doesn't have a success flag,
         * add one and send to debug client?
         */
        duk_debug_write_reply(thr);
        duk_debug_write_eom(thr);
}

DUK_LOCAL void duk__debug_handle_get_call_stack(duk_hthread *thr, duk_heap *heap) {
        duk_context *ctx = (duk_context *) thr;
        duk_hthread *curr_thr = thr;
        duk_activation *curr_act;
        duk_uint_fast32_t pc;
        duk_uint_fast32_t line;
        duk_size_t i;

        DUK_ASSERT(thr != NULL);
        DUK_UNREF(heap);

        duk_debug_write_reply(thr);
        while (curr_thr != NULL) {
                i = curr_thr->callstack_top;
                while (i > 0) {
                        i--;
                        curr_act = curr_thr->callstack + i;

                        /* PC/line semantics here are:
                         *   - For callstack top we're conceptually between two
                         *     opcodes and current PC indicates next line to
                         *     execute, so report that (matches Status).
                         *   - For other activations we're conceptually still
                         *     executing the instruction at PC-1, so report that
                         *     (matches error stacktrace behavior).
                         *   - See: https://github.com/svaarala/duktape/issues/281
                         */

                        /* XXX: optimize to use direct reads, i.e. avoid
                         * value stack operations.
                         */
                        duk_push_tval(ctx, &curr_act->tv_func);
                        duk_get_prop_stridx(ctx, -1, DUK_STRIDX_FILE_NAME);
                        duk__debug_write_hstring_safe_top(thr);
                        duk_get_prop_stridx(ctx, -2, DUK_STRIDX_NAME);
                        duk__debug_write_hstring_safe_top(thr);
                        pc = duk_hthread_get_act_curr_pc(thr, curr_act);
                        if (i != curr_thr->callstack_top - 1 && pc > 0) {
                                pc--;
                        }
                        line = duk_hobject_pc2line_query(ctx, -3, pc);
                        duk_debug_write_uint(thr, (duk_uint32_t) line);
                        duk_debug_write_uint(thr, (duk_uint32_t) pc);
                        duk_pop_3(ctx);
                }
                curr_thr = curr_thr->resumer;
        }
        /* SCANBUILD: warning about 'thr' potentially being NULL here,
         * warning is incorrect because thr != NULL always here.
         */
        duk_debug_write_eom(thr);
}

DUK_LOCAL void duk__debug_handle_get_locals(duk_hthread *thr, duk_heap *heap) {
        duk_context *ctx = (duk_context *) thr;
        duk_activation *curr_act;
        duk_int32_t level;
        duk_hstring *varname;

        DUK_UNREF(heap);

        if (duk_debug_peek_byte(thr) != DUK_DBG_IB_EOM) {
                level = duk_debug_read_int(thr);  /* optional callstack level */
                if (level >= 0 || -level > (duk_int32_t) thr->callstack_top) {
                        DUK_D(DUK_DPRINT("invalid callstack level for GetLocals"));
                        duk_debug_write_error_eom(thr, DUK_DBG_ERR_NOTFOUND, "invalid callstack level");
                        return;
                }
                duk_debug_write_reply(thr);
        } else {
                duk_debug_write_reply(thr);
                if (thr->callstack_top == 0) {
                        goto callstack_empty;
                }
                level = -1;
        }

        curr_act = thr->callstack + thr->callstack_top + level;

        /* XXX: several nice-to-have improvements here:
         *   - Use direct reads avoiding value stack operations
         *   - Avoid triggering getters, indicate getter values to debug client
         *   - If side effects are possible, add error catching
         */

        duk_push_tval(ctx, &curr_act->tv_func);
        duk_get_prop_stridx(ctx, -1, DUK_STRIDX_INT_VARMAP);
        if (duk_is_object(ctx, -1)) {
                duk_enum(ctx, -1, 0 /*enum_flags*/);
                while (duk_next(ctx, -1 /*enum_index*/, 0 /*get_value*/)) {
                        varname = duk_get_hstring(ctx, -1);
                        DUK_ASSERT(varname != NULL);

                        duk_js_getvar_activation(thr, curr_act, varname, 0 /*throw_flag*/);
                        /* [ ... func varmap enum key value this ] */
                        duk_debug_write_hstring(thr, duk_get_hstring(ctx, -3));
                        duk_debug_write_tval(thr, duk_get_tval(ctx, -2));
                        duk_pop_3(ctx);  /* -> [ ... func varmap enum ] */
                }
        } else {
                DUK_D(DUK_DPRINT("varmap is not an object in GetLocals, ignore"));
        }

 callstack_empty:
        duk_debug_write_eom(thr);
}

DUK_LOCAL void duk__debug_handle_eval(duk_hthread *thr, duk_heap *heap) {
        duk_context *ctx = (duk_context *) thr;
        duk_small_uint_t call_flags;
        duk_int_t call_ret;
        duk_small_int_t eval_err;
        duk_int32_t level;

        DUK_UNREF(heap);

        DUK_D(DUK_DPRINT("debug command Eval"));

        /* The eval code is executed within the lexical environment of a specified
         * activation.  For now, use global object eval() function, with the eval
         * considered a 'direct call to eval'.
         *
         * Callstack level for debug commands only affects scope -- the callstack
         * as seen by, e.g. Duktape.act() will be the same regardless.
         */

        /* nargs == 2 so we can pass a callstack level to eval(). */
        duk_push_c_function(ctx, duk_bi_global_object_eval, 2 /*nargs*/);
        duk_push_undefined(ctx);  /* 'this' binding shouldn't matter here */

        (void) duk_debug_read_hstring(thr);
        if (duk_debug_peek_byte(thr) != DUK_DBG_IB_EOM) {
                level = duk_debug_read_int(thr);  /* optional callstack level */
                if (level >= 0 || -level > (duk_int32_t) thr->callstack_top) {
                        DUK_D(DUK_DPRINT("invalid callstack level for Eval"));
                        duk_debug_write_error_eom(thr, DUK_DBG_ERR_NOTFOUND, "invalid callstack level");
                        return;
                }
        }
        else {
                level = -1;
        }
        DUK_ASSERT(level < 0 && -level <= (duk_int32_t) thr->callstack_top);
        duk_push_int(ctx, level - 1);  /* compensate for eval() call */

        /* [ ... eval "eval" eval_input level ] */

        call_flags = 0;
        if (thr->callstack_top >= (duk_size_t) -level) {
                duk_activation *act;
                duk_hobject *fun;

                act = thr->callstack + thr->callstack_top + level;
                fun = DUK_ACT_GET_FUNC(act);
                if (fun != NULL && DUK_HOBJECT_IS_COMPILEDFUNCTION(fun)) {
                        /* Direct eval requires that there's a current
                         * activation and it is an Ecmascript function.
                         * When Eval is executed from e.g. cooperate API
                         * call we'll need to do an indirect eval instead.
                         */
                        call_flags |= DUK_CALL_FLAG_DIRECT_EVAL;
                }
        }

        call_ret = duk_handle_call_protected(thr, 2 /*num_stack_args*/, call_flags);

        if (call_ret == DUK_EXEC_SUCCESS) {
                eval_err = 0;
                /* Use result value as is. */
        } else {
                /* For errors a string coerced result is most informative
                 * right now, as the debug client doesn't have the capability
                 * to traverse the error object.
                 */
                eval_err = 1;
                duk_safe_to_string(ctx, -1);
        }

        /* [ ... result ] */

        duk_debug_write_reply(thr);
        duk_debug_write_int(thr, (duk_int32_t) eval_err);
        DUK_ASSERT(duk_get_tval(ctx, -1) != NULL);
        duk_debug_write_tval(thr, duk_get_tval(ctx, -1));
        duk_debug_write_eom(thr);
}

DUK_LOCAL void duk__debug_handle_detach(duk_hthread *thr, duk_heap *heap) {
        DUK_UNREF(heap);
        DUK_D(DUK_DPRINT("debug command Detach"));

        duk_debug_write_reply(thr);
        duk_debug_write_eom(thr);

        DUK_D(DUK_DPRINT("debug connection detached, mark broken"));
        DUK__SET_CONN_BROKEN(thr, 0);  /* not an error */
}

DUK_LOCAL void duk__debug_handle_apprequest(duk_hthread *thr, duk_heap *heap) {
        duk_context *ctx = (duk_context *) thr;
        duk_idx_t old_top;

        DUK_D(DUK_DPRINT("debug command AppRequest"));

        old_top = duk_get_top(ctx);  /* save stack top */

        if (heap->dbg_request_cb != NULL) {
                duk_idx_t nrets;
                duk_idx_t nvalues = 0;
                duk_idx_t top, idx;

                /* Read tvals from the message and push them onto the valstack,
                 * then call the request callback to process the request.
                 */
                while (duk_debug_peek_byte(thr) != DUK_DBG_IB_EOM) {
                        duk_tval *tv;
                        if (!duk_check_stack(ctx, 1)) {
                                DUK_D(DUK_DPRINT("failed to allocate space for request dvalue(s)"));
                                goto fail;
                        }
                        tv = duk_debug_read_tval(thr);  /* push to stack */
                        if (tv == NULL) {
                                /* detached */
                                return;
                        }
                        nvalues++;
                }
                DUK_ASSERT(duk_get_top(ctx) == old_top + nvalues);

                /* Request callback should push values for reply to client onto valstack */
                DUK_D(DUK_DPRINT("calling into AppRequest request_cb with nvalues=%ld, old_top=%ld, top=%ld",
                                 (long) nvalues, (long) old_top, (long) duk_get_top(ctx)));
                nrets = heap->dbg_request_cb(ctx, heap->dbg_udata, nvalues);
                DUK_D(DUK_DPRINT("returned from AppRequest request_cb; nvalues=%ld -> nrets=%ld, old_top=%ld, top=%ld",
                                 (long) nvalues, (long) nrets, (long) old_top, (long) duk_get_top(ctx)));
                if (nrets >= 0) {
                        DUK_ASSERT(duk_get_top(ctx) >= old_top + nrets);
                        if (duk_get_top(ctx) < old_top + nrets) {
                                DUK_D(DUK_DPRINT("AppRequest callback doesn't match value stack configuration, "
                                                 "top=%ld < old_top=%ld + nrets=%ld; "
                                                 "this might mean it's unsafe to continue!",
                                                 (long) duk_get_top(ctx), (long) old_top, (long) nrets));
                                goto fail;
                        }

                        /* Reply with tvals pushed by request callback */
                        duk_debug_write_byte(thr, DUK_DBG_IB_REPLY);
                        top = duk_get_top(ctx);
                        for (idx = top - nrets; idx < top; idx++) {
                                duk_debug_write_tval(thr, DUK_GET_TVAL_POSIDX(ctx, idx));
                        }
                        duk_debug_write_eom(thr);
                } else {
                        DUK_ASSERT(duk_get_top(ctx) >= old_top + 1);
                        if (duk_get_top(ctx) < old_top + 1) {
                                DUK_D(DUK_DPRINT("request callback return value doesn't match value stack configuration"));
                                goto fail;
                        }
                        duk_debug_write_error_eom(thr, DUK_DBG_ERR_APPLICATION, duk_get_string(ctx, -1));
                }

                duk_set_top(ctx, old_top);  /* restore stack top */
        } else {
                DUK_D(DUK_DPRINT("no request callback, treat AppRequest as unsupported"));
                duk_debug_write_error_eom(thr, DUK_DBG_ERR_UNSUPPORTED, "AppRequest unsupported by target");
        }

        return;

 fail:
        duk_set_top(ctx, old_top);  /* restore stack top */
        DUK__SET_CONN_BROKEN(thr, 1);
}

/*
 *  DumpHeap command
 */

#if defined(DUK_USE_DEBUGGER_DUMPHEAP)
/* XXX: this has some overlap with object inspection; remove this and make
 * DumpHeap return lists of heapptrs instead?
 */
DUK_LOCAL void duk__debug_dump_heaphdr(duk_hthread *thr, duk_heap *heap, duk_heaphdr *hdr) {
        DUK_UNREF(heap);

        duk_debug_write_heapptr(thr, hdr);
        duk_debug_write_uint(thr, (duk_uint32_t) DUK_HEAPHDR_GET_TYPE(hdr));
        duk_debug_write_uint(thr, (duk_uint32_t) DUK_HEAPHDR_GET_FLAGS_RAW(hdr));
#if defined(DUK_USE_REFERENCE_COUNTING)
        duk_debug_write_uint(thr, (duk_uint32_t) DUK_HEAPHDR_GET_REFCOUNT(hdr));
#else
        duk_debug_write_int(thr, (duk_int32_t) -1);
#endif

        switch (DUK_HEAPHDR_GET_TYPE(hdr)) {
        case DUK_HTYPE_STRING: {
                duk_hstring *h = (duk_hstring *) hdr;

                duk_debug_write_uint(thr, (duk_int32_t) DUK_HSTRING_GET_BYTELEN(h));
                duk_debug_write_uint(thr, (duk_int32_t) DUK_HSTRING_GET_CHARLEN(h));
                duk_debug_write_uint(thr, (duk_int32_t) DUK_HSTRING_GET_HASH(h));
                duk_debug_write_hstring(thr, h);
                break;
        }
        case DUK_HTYPE_OBJECT: {
                duk_hobject *h = (duk_hobject *) hdr;
                duk_hstring *k;
                duk_uint_fast32_t i;

                duk_debug_write_uint(thr, (duk_uint32_t) DUK_HOBJECT_GET_CLASS_NUMBER(h));
                duk_debug_write_heapptr(thr, (duk_heaphdr *) DUK_HOBJECT_GET_PROTOTYPE(heap, h));
                duk_debug_write_uint(thr, (duk_uint32_t) DUK_HOBJECT_GET_ESIZE(h));
                duk_debug_write_uint(thr, (duk_uint32_t) DUK_HOBJECT_GET_ENEXT(h));
                duk_debug_write_uint(thr, (duk_uint32_t) DUK_HOBJECT_GET_ASIZE(h));
                duk_debug_write_uint(thr, (duk_uint32_t) DUK_HOBJECT_GET_HSIZE(h));

                for (i = 0; i < (duk_uint_fast32_t) DUK_HOBJECT_GET_ENEXT(h); i++) {
                        duk_debug_write_uint(thr, (duk_uint32_t) DUK_HOBJECT_E_GET_FLAGS(heap, h, i));
                        k = DUK_HOBJECT_E_GET_KEY(heap, h, i);
                        duk_debug_write_heapptr(thr, (duk_heaphdr *) k);
                        if (k == NULL) {
                                duk_debug_write_int(thr, 0);  /* isAccessor */
                                duk_debug_write_unused(thr);
                                continue;
                        }
                        if (DUK_HOBJECT_E_SLOT_IS_ACCESSOR(heap, h, i)) {
                                duk_debug_write_int(thr, 1);  /* isAccessor */
                                duk_debug_write_heapptr(thr, (duk_heaphdr *) DUK_HOBJECT_E_GET_VALUE_PTR(heap, h, i)->a.get);
                                duk_debug_write_heapptr(thr, (duk_heaphdr *) DUK_HOBJECT_E_GET_VALUE_PTR(heap, h, i)->a.set);
                        } else {
                                duk_debug_write_int(thr, 0);  /* isAccessor */

                                duk__debug_write_tval_heapptr(thr, &DUK_HOBJECT_E_GET_VALUE_PTR(heap, h, i)->v);
                        }
                }

                for (i = 0; i < (duk_uint_fast32_t) DUK_HOBJECT_GET_ASIZE(h); i++) {
                        /* Note: array dump will include elements beyond
                         * 'length'.
                         */
                        duk__debug_write_tval_heapptr(thr, DUK_HOBJECT_A_GET_VALUE_PTR(heap, h, i));
                }
                break;
        }
        case DUK_HTYPE_BUFFER: {
                duk_hbuffer *h = (duk_hbuffer *) hdr;

                duk_debug_write_uint(thr, (duk_uint32_t) DUK_HBUFFER_GET_SIZE(h));
                duk_debug_write_buffer(thr, (const char *) DUK_HBUFFER_GET_DATA_PTR(heap, h), (duk_size_t) DUK_HBUFFER_GET_SIZE(h));
                break;
        }
        default: {
                DUK_D(DUK_DPRINT("invalid htype: %d", (int) DUK_HEAPHDR_GET_TYPE(hdr)));
        }
        }
}

DUK_LOCAL void duk__debug_dump_heap_allocated(duk_hthread *thr, duk_heap *heap) {
        duk_heaphdr *hdr;

        hdr = heap->heap_allocated;
        while (hdr != NULL) {
                duk__debug_dump_heaphdr(thr, heap, hdr);
                hdr = DUK_HEAPHDR_GET_NEXT(heap, hdr);
        }
}

#if defined(DUK_USE_STRTAB_CHAIN)
DUK_LOCAL void duk__debug_dump_strtab_chain(duk_hthread *thr, duk_heap *heap) {
        duk_uint_fast32_t i, j;
        duk_strtab_entry *e;
#if defined(DUK_USE_HEAPPTR16)
        duk_uint16_t *lst;
#else
        duk_hstring **lst;
#endif
        duk_hstring *h;

        for (i = 0; i < DUK_STRTAB_CHAIN_SIZE; i++) {
                e = heap->strtable + i;
                if (e->listlen > 0) {
#if defined(DUK_USE_HEAPPTR16)
                        lst = (duk_uint16_t *) DUK_USE_HEAPPTR_DEC16(heap->heap_udata, e->u.strlist16);
#else
                        lst = e->u.strlist;
#endif
                        DUK_ASSERT(lst != NULL);

                        for (j = 0; j < e->listlen; j++) {
#if defined(DUK_USE_HEAPPTR16)
                                h = DUK_USE_HEAPPTR_DEC16(heap->heap_udata, lst[j]);
#else
                                h = lst[j];
#endif
                                if (h != NULL) {
                                        duk__debug_dump_heaphdr(thr, heap, (duk_heaphdr *) h);
                                }
                        }
                } else {
#if defined(DUK_USE_HEAPPTR16)
                        h = DUK_USE_HEAPPTR_DEC16(heap->heap_udata, e->u.str16);
#else
                        h = e->u.str;
#endif
                        if (h != NULL) {
                                duk__debug_dump_heaphdr(thr, heap, (duk_heaphdr *) h);
                        }
                }
        }
}
#endif  /* DUK_USE_STRTAB_CHAIN */

#if defined(DUK_USE_STRTAB_PROBE)
DUK_LOCAL void duk__debug_dump_strtab_probe(duk_hthread *thr, duk_heap *heap) {
        duk_uint32_t i;
        duk_hstring *h;

        for (i = 0; i < heap->st_size; i++) {
#if defined(DUK_USE_HEAPPTR16)
                h = DUK_USE_HEAPPTR_DEC16(heap->heap_udata, heap->strtable16[i]);
#else
                h = heap->strtable[i];
#endif
                if (h == NULL || h == DUK_STRTAB_DELETED_MARKER(heap)) {
                        continue;
                }

                duk__debug_dump_heaphdr(thr, heap, (duk_heaphdr *) h);
        }
}
#endif  /* DUK_USE_STRTAB_PROBE */

DUK_LOCAL void duk__debug_handle_dump_heap(duk_hthread *thr, duk_heap *heap) {
        DUK_D(DUK_DPRINT("debug command DumpHeap"));

        duk_debug_write_reply(thr);
        duk__debug_dump_heap_allocated(thr, heap);
#if defined(DUK_USE_STRTAB_CHAIN)
        duk__debug_dump_strtab_chain(thr, heap);
#endif
#if defined(DUK_USE_STRTAB_PROBE)
        duk__debug_dump_strtab_probe(thr, heap);
#endif
        duk_debug_write_eom(thr);
}
#endif  /* DUK_USE_DEBUGGER_DUMPHEAP */

DUK_LOCAL void duk__debug_handle_get_bytecode(duk_hthread *thr, duk_heap *heap) {
        duk_activation *act;
        duk_hcompiledfunction *fun = NULL;
        duk_size_t i, n;
        duk_tval *tv;
        duk_hobject **fn;
        duk_int32_t level = -1;
        duk_uint8_t ibyte;

        DUK_UNREF(heap);

        DUK_D(DUK_DPRINT("debug command GetBytecode"));

        ibyte = duk_debug_peek_byte(thr);
        if (ibyte != DUK_DBG_IB_EOM) {
                tv = duk_debug_read_tval(thr);
                if (tv == NULL) {
                        /* detached */
                        return;
                }
                if (DUK_TVAL_IS_OBJECT(tv)) {
                        /* tentative, checked later */
                        fun = (duk_hcompiledfunction *) DUK_TVAL_GET_OBJECT(tv);
                        DUK_ASSERT(fun != NULL);
                } else if (DUK_TVAL_IS_NUMBER(tv)) {
                        level = (duk_int32_t) DUK_TVAL_GET_NUMBER(tv);
                } else {
                        DUK_D(DUK_DPRINT("invalid argument to GetBytecode: %!T", tv));
                        goto fail_args;
                }
        }

        if (fun == NULL) {
                if (level >= 0 || -level > (duk_int32_t) thr->callstack_top) {
                        DUK_D(DUK_DPRINT("invalid callstack level for GetBytecode"));
                        goto fail_level;
                }
                act = thr->callstack + thr->callstack_top + level;
                fun = (duk_hcompiledfunction *) DUK_ACT_GET_FUNC(act);
        }

        if (fun == NULL || !DUK_HOBJECT_IS_COMPILEDFUNCTION((duk_hobject *) fun)) {
                DUK_D(DUK_DPRINT("invalid argument to GetBytecode: %!O", fun));
                goto fail_args;
        }
        DUK_ASSERT(fun != NULL && DUK_HOBJECT_IS_COMPILEDFUNCTION((duk_hobject *) fun));

        duk_debug_write_reply(thr);
        n = DUK_HCOMPILEDFUNCTION_GET_CONSTS_COUNT(heap, fun);
        duk_debug_write_int(thr, (duk_int32_t) n);
        tv = DUK_HCOMPILEDFUNCTION_GET_CONSTS_BASE(heap, fun);
        for (i = 0; i < n; i++) {
                duk_debug_write_tval(thr, tv);
                tv++;
        }
        n = DUK_HCOMPILEDFUNCTION_GET_FUNCS_COUNT(heap, fun);
        duk_debug_write_int(thr, (duk_int32_t) n);
        fn = DUK_HCOMPILEDFUNCTION_GET_FUNCS_BASE(heap, fun);
        for (i = 0; i < n; i++) {
                duk_debug_write_hobject(thr, *fn);
                fn++;
        }
        duk_debug_write_string(thr,
                               (const char *) DUK_HCOMPILEDFUNCTION_GET_CODE_BASE(heap, fun),
                               (duk_size_t) DUK_HCOMPILEDFUNCTION_GET_CODE_SIZE(heap, fun));
        duk_debug_write_eom(thr);
        return;

 fail_args:
        duk_debug_write_error_eom(thr, DUK_DBG_ERR_UNKNOWN, "invalid argument");
        return;

 fail_level:
        duk_debug_write_error_eom(thr, DUK_DBG_ERR_NOTFOUND, "invalid callstack level");
        return;
}

/*
 *  Object inspection commands: GetHeapObjInfo, GetObjPropDesc,
 *  GetObjPropDescRange
 */

#if defined(DUK_USE_DEBUGGER_INSPECT)

#if 0 /* pruned */
DUK_LOCAL const char * const duk__debug_getinfo_heaphdr_keys[] = {
        "reachable",
        "temproot",
        "finalizable",
        "finalized",
        "readonly"
        /* NULL not needed here */
};
DUK_LOCAL duk_uint_t duk__debug_getinfo_heaphdr_masks[] = {
        DUK_HEAPHDR_FLAG_REACHABLE,
        DUK_HEAPHDR_FLAG_TEMPROOT,
        DUK_HEAPHDR_FLAG_FINALIZABLE,
        DUK_HEAPHDR_FLAG_FINALIZED,
        DUK_HEAPHDR_FLAG_READONLY,
        0  /* terminator */
};
#endif
DUK_LOCAL const char * const duk__debug_getinfo_hstring_keys[] = {
#if 0
        "arridx",
        "internal",
        "reserved_word",
        "strict_reserved_word",
        "eval_or_arguments",
#endif
        "extdata"
        /* NULL not needed here */
};
DUK_LOCAL duk_uint_t duk__debug_getinfo_hstring_masks[] = {
#if 0
        DUK_HSTRING_FLAG_ARRIDX,
        DUK_HSTRING_FLAG_INTERNAL,
        DUK_HSTRING_FLAG_RESERVED_WORD,
        DUK_HSTRING_FLAG_STRICT_RESERVED_WORD,
        DUK_HSTRING_FLAG_EVAL_OR_ARGUMENTS,
#endif
        DUK_HSTRING_FLAG_EXTDATA,
        0  /* terminator */
};
DUK_LOCAL const char * const duk__debug_getinfo_hobject_keys[] = {
        "extensible",
        "constructable",
        "bound",
        "compiledfunction",
        "nativefunction",
        "bufferobject",
        "thread",
        "array_part",
        "strict",
        "notail",
        "newenv",
        "namebinding",
        "createargs",
        "envrecclosed",
        "exotic_array",
        "exotic_stringobj",
        "exotic_arguments",
        "exotic_dukfunc",
        "exotic_proxyobj"
        /* NULL not needed here */
};
DUK_LOCAL duk_uint_t duk__debug_getinfo_hobject_masks[] = {
        DUK_HOBJECT_FLAG_EXTENSIBLE,
        DUK_HOBJECT_FLAG_CONSTRUCTABLE,
        DUK_HOBJECT_FLAG_BOUND,
        DUK_HOBJECT_FLAG_COMPILEDFUNCTION,
        DUK_HOBJECT_FLAG_NATIVEFUNCTION,
        DUK_HOBJECT_FLAG_BUFFEROBJECT,
        DUK_HOBJECT_FLAG_THREAD,
        DUK_HOBJECT_FLAG_ARRAY_PART,
        DUK_HOBJECT_FLAG_STRICT,
        DUK_HOBJECT_FLAG_NOTAIL,
        DUK_HOBJECT_FLAG_NEWENV,
        DUK_HOBJECT_FLAG_NAMEBINDING,
        DUK_HOBJECT_FLAG_CREATEARGS,
        DUK_HOBJECT_FLAG_ENVRECCLOSED,
        DUK_HOBJECT_FLAG_EXOTIC_ARRAY,
        DUK_HOBJECT_FLAG_EXOTIC_STRINGOBJ,
        DUK_HOBJECT_FLAG_EXOTIC_ARGUMENTS,
        DUK_HOBJECT_FLAG_EXOTIC_DUKFUNC,
        DUK_HOBJECT_FLAG_EXOTIC_PROXYOBJ,
        0  /* terminator */
};
DUK_LOCAL const char * const duk__debug_getinfo_hbuffer_keys[] = {
        "dynamic",
        "external"
        /* NULL not needed here */
};
DUK_LOCAL duk_uint_t duk__debug_getinfo_hbuffer_masks[] = {
        DUK_HBUFFER_FLAG_DYNAMIC,
        DUK_HBUFFER_FLAG_EXTERNAL,
        0  /* terminator */
};

DUK_LOCAL void duk__debug_getinfo_flags_key(duk_hthread *thr, const char *key) {
        duk_debug_write_uint(thr, 0);
        duk_debug_write_cstring(thr, key);
}

DUK_LOCAL void duk__debug_getinfo_prop_uint(duk_hthread *thr, const char *key, duk_uint_t val) {
        duk_debug_write_uint(thr, 0);
        duk_debug_write_cstring(thr, key);
        duk_debug_write_uint(thr, val);
}

DUK_LOCAL void duk__debug_getinfo_prop_int(duk_hthread *thr, const char *key, duk_int_t val) {
        duk_debug_write_uint(thr, 0);
        duk_debug_write_cstring(thr, key);
        duk_debug_write_int(thr, val);
}

DUK_LOCAL void duk__debug_getinfo_prop_bool(duk_hthread *thr, const char *key, duk_bool_t val) {
        duk_debug_write_uint(thr, 0);
        duk_debug_write_cstring(thr, key);
        duk_debug_write_boolean(thr, val);
}

DUK_LOCAL void duk__debug_getinfo_bitmask(duk_hthread *thr, const char * const * keys, duk_uint_t *masks, duk_uint_t flags) {
        const char *key;
        duk_uint_t mask;

        for (;;) {
                mask = *masks++;
                if (!mask) {
                        break;
                }
                key = *keys++;
                DUK_ASSERT(key != NULL);

                DUK_DD(DUK_DDPRINT("inspect bitmask: key=%s, mask=0x%08lx, flags=0x%08lx", key, (unsigned long) mask, (unsigned long) flags));
                duk__debug_getinfo_prop_bool(thr, key, flags & mask);
        }
}

/* Inspect a property using a virtual index into a conceptual property list
 * consisting of (1) all array part items from [0,a_size[ (even when above
 * .length) and (2) all entry part items from [0,e_next[.  Unused slots are
 * indicated using dvalue 'unused'.
 */
DUK_LOCAL duk_bool_t duk__debug_getprop_index(duk_hthread *thr, duk_heap *heap, duk_hobject *h_obj, duk_uint_t idx) {
        duk_uint_t a_size;
        duk_tval *tv;
        duk_hstring *h_key;
        duk_hobject *h_getset;
        duk_uint_t flags;

        DUK_UNREF(heap);

        a_size = DUK_HOBJECT_GET_ASIZE(h_obj);
        if (idx < a_size) {
                duk_debug_write_uint(thr, DUK_PROPDESC_FLAGS_WEC);
                duk_debug_write_uint(thr, idx);
                tv = DUK_HOBJECT_A_GET_VALUE_PTR(heap, h_obj, idx);
                duk_debug_write_tval(thr, tv);
                return 1;
        }

        idx -= a_size;
        if (idx >= DUK_HOBJECT_GET_ENEXT(h_obj)) {
                return 0;
        }

        h_key = DUK_HOBJECT_E_GET_KEY(heap, h_obj, idx);
        if (h_key == NULL) {
                duk_debug_write_uint(thr, 0);
                duk_debug_write_null(thr);
                duk_debug_write_unused(thr);
                return 1;
        }

        flags = DUK_HOBJECT_E_GET_FLAGS(heap, h_obj, idx);
        if (DUK_HSTRING_HAS_INTERNAL(h_key)) {
                flags |= DUK_DBG_PROPFLAG_INTERNAL;
        }
        duk_debug_write_uint(thr, flags);
        duk_debug_write_hstring(thr, h_key);
        if (flags & DUK_PROPDESC_FLAG_ACCESSOR) {
                h_getset = DUK_HOBJECT_E_GET_VALUE_GETTER(heap, h_obj, idx);
                if (h_getset) {
                        duk_debug_write_hobject(thr, h_getset);
                } else {
                        duk_debug_write_null(thr);
                }
                h_getset = DUK_HOBJECT_E_GET_VALUE_SETTER(heap, h_obj, idx);
                if (h_getset) {
                        duk_debug_write_hobject(thr, h_getset);
                } else {
                        duk_debug_write_null(thr);
                }
        } else {
                tv = DUK_HOBJECT_E_GET_VALUE_TVAL_PTR(heap, h_obj, idx);
                duk_debug_write_tval(thr, tv);
        }
        return 1;
}

DUK_LOCAL void duk__debug_handle_get_heap_obj_info(duk_hthread *thr, duk_heap *heap) {
        duk_heaphdr *h;

        DUK_D(DUK_DPRINT("debug command GetHeapObjInfo"));
        DUK_UNREF(heap);

        h = duk_debug_read_any_ptr(thr);
        if (!h) {
                duk_debug_write_error_eom(thr, DUK_DBG_ERR_UNKNOWN, "invalid target");
                return;
        }

        duk_debug_write_reply(thr);

        /* As with all inspection code, we rely on the debug client providing
         * a valid, non-stale pointer: there's no portable way to safely
         * validate the pointer here.
         */

        duk__debug_getinfo_flags_key(thr, "heapptr");
        duk_debug_write_heapptr(thr, h);

        /* XXX: comes out as signed now */
        duk__debug_getinfo_prop_uint(thr, "heaphdr_flags", (duk_uint_t) DUK_HEAPHDR_GET_FLAGS(h));
        duk__debug_getinfo_prop_uint(thr, "heaphdr_type", (duk_uint_t) DUK_HEAPHDR_GET_TYPE(h));
#if defined(DUK_USE_REFERENCE_COUNTING)
        duk__debug_getinfo_prop_uint(thr, "refcount", (duk_uint_t) DUK_HEAPHDR_GET_REFCOUNT(h));
#endif
#if 0 /* pruned */
        duk__debug_getinfo_bitmask(thr,
                                   duk__debug_getinfo_heaphdr_keys,
                                   duk__debug_getinfo_heaphdr_masks,
                                   DUK_HEAPHDR_GET_FLAGS_RAW(h));
#endif

        switch (DUK_HEAPHDR_GET_TYPE(h)) {
        case DUK_HTYPE_STRING: {
                duk_hstring *h_str;

                h_str = (duk_hstring *) h;
                duk__debug_getinfo_bitmask(thr,
                                           duk__debug_getinfo_hstring_keys,
                                           duk__debug_getinfo_hstring_masks,
                                           DUK_HEAPHDR_GET_FLAGS_RAW(h));
                duk__debug_getinfo_prop_uint(thr, "bytelen", DUK_HSTRING_GET_BYTELEN(h_str));
                duk__debug_getinfo_prop_uint(thr, "charlen", DUK_HSTRING_GET_CHARLEN(h_str));
                duk__debug_getinfo_prop_uint(thr, "hash", DUK_HSTRING_GET_HASH(h_str));
                duk__debug_getinfo_flags_key(thr, "data");
                duk_debug_write_hstring(thr, h_str);
                break;
        }
        case DUK_HTYPE_OBJECT: {
                duk_hobject *h_obj;
                duk_hobject *h_proto;

                h_obj = (duk_hobject *) h;
                h_proto = DUK_HOBJECT_GET_PROTOTYPE(heap, h_obj);

                /* duk_hobject specific fields. */
                duk__debug_getinfo_bitmask(thr,
                                           duk__debug_getinfo_hobject_keys,
                                           duk__debug_getinfo_hobject_masks,
                                           DUK_HEAPHDR_GET_FLAGS_RAW(h));
                duk__debug_getinfo_prop_uint(thr, "class_number", DUK_HOBJECT_GET_CLASS_NUMBER(h_obj));
                duk__debug_getinfo_flags_key(thr, "class_name");
                duk_debug_write_hstring(thr, DUK_HOBJECT_GET_CLASS_STRING(heap, h_obj));
                duk__debug_getinfo_flags_key(thr, "prototype");
                if (h_proto != NULL) {
                        duk_debug_write_hobject(thr, h_proto);
                } else {
                        duk_debug_write_null(thr);
                }
                duk__debug_getinfo_flags_key(thr, "props");
                duk_debug_write_pointer(thr, (void *) DUK_HOBJECT_GET_PROPS(heap, h_obj));
                duk__debug_getinfo_prop_uint(thr, "e_size", (duk_uint_t) DUK_HOBJECT_GET_ESIZE(h_obj));
                duk__debug_getinfo_prop_uint(thr, "e_next", (duk_uint_t) DUK_HOBJECT_GET_ENEXT(h_obj));
                duk__debug_getinfo_prop_uint(thr, "a_size", (duk_uint_t) DUK_HOBJECT_GET_ASIZE(h_obj));
                duk__debug_getinfo_prop_uint(thr, "h_size", (duk_uint_t) DUK_HOBJECT_GET_HSIZE(h_obj));

                /* duk_hnativefunction specific fields. */
                if (DUK_HOBJECT_IS_NATIVEFUNCTION(h_obj)) {
                        duk_hnativefunction *h_fun;
                        h_fun = (duk_hnativefunction *) h_obj;

                        duk__debug_getinfo_prop_int(thr, "nargs", h_fun->nargs);
                        duk__debug_getinfo_prop_int(thr, "magic", h_fun->magic);
                        duk__debug_getinfo_prop_bool(thr, "varargs", h_fun->magic == DUK_HNATIVEFUNCTION_NARGS_VARARGS);
                        /* Native function pointer may be different from a void pointer,
                         * and we serialize it from memory directly now (no byte swapping etc).
                         */
                        duk__debug_getinfo_flags_key(thr, "funcptr");
                        duk_debug_write_buffer(thr, (const char *) &h_fun->func, sizeof(h_fun->func));
                }

                if (DUK_HOBJECT_IS_COMPILEDFUNCTION(h_obj)) {
                        duk_hcompiledfunction *h_fun;
                        duk_hbuffer *h_buf;
                        h_fun = (duk_hcompiledfunction *) h_obj;

                        duk__debug_getinfo_prop_int(thr, "nregs", h_fun->nregs);
                        duk__debug_getinfo_prop_int(thr, "nargs", h_fun->nargs);
                        duk__debug_getinfo_prop_uint(thr, "start_line", h_fun->start_line);
                        duk__debug_getinfo_prop_uint(thr, "end_line", h_fun->end_line);
                        h_buf = (duk_hbuffer *) DUK_HCOMPILEDFUNCTION_GET_DATA(thr->heap, h_fun);
                        if (h_buf != NULL) {
                                duk__debug_getinfo_flags_key(thr, "data");
                                duk_debug_write_heapptr(thr, (duk_heaphdr *) h_buf);
                        }
                }

                if (DUK_HOBJECT_IS_THREAD(h_obj)) {
                        /* XXX: Currently no inspection of threads, e.g. value stack, call
                         * stack, catch stack, etc.
                         */
                        duk_hthread *h_thr;
                        h_thr = (duk_hthread *) h_obj;
                        DUK_UNREF(h_thr);
                }

                if (DUK_HOBJECT_IS_BUFFEROBJECT(h_obj)) {
                        duk_hbufferobject *h_bufobj;
                        h_bufobj = (duk_hbufferobject *) h_obj;

                        duk__debug_getinfo_prop_uint(thr, "slice_offset", h_bufobj->offset);
                        duk__debug_getinfo_prop_uint(thr, "slice_length", h_bufobj->length);
                        duk__debug_getinfo_prop_uint(thr, "elem_shift", (duk_uint_t) h_bufobj->shift);
                        duk__debug_getinfo_prop_uint(thr, "elem_type", (duk_uint_t) h_bufobj->elem_type);
                        duk__debug_getinfo_prop_bool(thr, "is_view", (duk_uint_t) h_bufobj->is_view);
                        if (h_bufobj->buf != NULL) {
                                duk__debug_getinfo_flags_key(thr, "buffer");
                                duk_debug_write_heapptr(thr, (duk_heaphdr *) h_bufobj->buf);
                        }
                }
                break;
        }
        case DUK_HTYPE_BUFFER: {
                duk_hbuffer *h_buf;

                h_buf = (duk_hbuffer *) h;
                duk__debug_getinfo_bitmask(thr,
                                           duk__debug_getinfo_hbuffer_keys,
                                           duk__debug_getinfo_hbuffer_masks,
                                           DUK_HEAPHDR_GET_FLAGS_RAW(h));
                duk__debug_getinfo_prop_uint(thr, "size", (duk_uint_t) DUK_HBUFFER_GET_SIZE(h_buf));
                duk__debug_getinfo_flags_key(thr, "dataptr");
                duk_debug_write_pointer(thr, (void *) DUK_HBUFFER_GET_DATA_PTR(thr->heap, h_buf));
                duk__debug_getinfo_flags_key(thr, "data");
                duk_debug_write_hbuffer(thr, h_buf);  /* tolerates NULL h_buf */
                break;
        }
        default: {
                /* Since we already started writing the reply, just emit nothing. */
                DUK_D(DUK_DPRINT("inspect target pointer has invalid heaphdr type"));
        }
        }

        duk_debug_write_eom(thr);
}

DUK_LOCAL void duk__debug_handle_get_obj_prop_desc(duk_hthread *thr, duk_heap *heap) {
        duk_heaphdr *h;
        duk_hobject *h_obj;
        duk_hstring *h_key;
        duk_propdesc desc;

        DUK_D(DUK_DPRINT("debug command GetObjPropDesc"));
        DUK_UNREF(heap);

        h = duk_debug_read_any_ptr(thr);
        if (!h) {
                duk_debug_write_error_eom(thr, DUK_DBG_ERR_UNKNOWN, "invalid target");
                return;
        }
        h_key = duk_debug_read_hstring(thr);
        if (h == NULL || DUK_HEAPHDR_GET_TYPE(h) != DUK_HTYPE_OBJECT || h_key == NULL) {
                goto fail_args;
        }
        h_obj = (duk_hobject *) h;

        if (duk_hobject_get_own_propdesc(thr, h_obj, h_key, &desc, 0 /*flags*/)) {
                duk_int_t virtual_idx;
                duk_bool_t rc;

                /* To use the shared helper need the virtual index. */
                DUK_ASSERT(desc.e_idx >= 0 || desc.a_idx >= 0);
                virtual_idx = (desc.a_idx >= 0 ? desc.a_idx :
                               (duk_int_t) DUK_HOBJECT_GET_ASIZE(h_obj) + desc.e_idx);

                duk_debug_write_reply(thr);
                rc = duk__debug_getprop_index(thr, heap, h_obj, (duk_uint_t) virtual_idx);
                DUK_ASSERT(rc == 1);
                DUK_UNREF(rc);
                duk_debug_write_eom(thr);
        } else {
                duk_debug_write_error_eom(thr, DUK_DBG_ERR_NOTFOUND, "not found");
        }
        return;

 fail_args:
        duk_debug_write_error_eom(thr, DUK_DBG_ERR_UNKNOWN, "invalid args");
}

DUK_LOCAL void duk__debug_handle_get_obj_prop_desc_range(duk_hthread *thr, duk_heap *heap) {
        duk_heaphdr *h;
        duk_hobject *h_obj;
        duk_uint_t idx, idx_start, idx_end;

        DUK_D(DUK_DPRINT("debug command GetObjPropDescRange"));
        DUK_UNREF(heap);

        h = duk_debug_read_any_ptr(thr);
        idx_start = duk_debug_read_int(thr);
        idx_end = duk_debug_read_int(thr);
        if (h == NULL || DUK_HEAPHDR_GET_TYPE(h) != DUK_HTYPE_OBJECT) {
                goto fail_args;
        }
        h_obj = (duk_hobject *) h;

        /* The index range space is conceptually the array part followed by the
         * entry part.  Unlike normal enumeration all slots are exposed here as
         * is and return 'unused' if the slots are not in active use.  In particular
         * the array part is included for the full a_size regardless of what the
         * array .length is.
         */

        duk_debug_write_reply(thr);
        for (idx = idx_start; idx < idx_end; idx++) {
                if (!duk__debug_getprop_index(thr, heap, h_obj, idx)) {
                        break;
                }
        }
        duk_debug_write_eom(thr);
        return;

 fail_args:
        duk_debug_write_error_eom(thr, DUK_DBG_ERR_UNKNOWN, "invalid args");
}

#endif  /* DUK_USE_DEBUGGER_INSPECT */

/*
 *  Process incoming debug requests
 *
 *  Individual request handlers can push temporaries on the value stack and
 *  rely on duk__debug_process_message() to restore the value stack top
 *  automatically.
 */

/* Process one debug message.  Automatically restore value stack top to its
 * entry value, so that individual message handlers don't need exact value
 * stack handling which is convenient.
 */
DUK_LOCAL void duk__debug_process_message(duk_hthread *thr) {
        duk_context *ctx = (duk_context *) thr;
        duk_heap *heap;
        duk_uint8_t x;
        duk_int32_t cmd;
        duk_idx_t entry_top;

        DUK_ASSERT(thr != NULL);
        heap = thr->heap;
        DUK_ASSERT(heap != NULL);
        DUK_UNREF(ctx);

        entry_top = duk_get_top(ctx);

        x = duk_debug_read_byte(thr);
        switch (x) {
        case DUK_DBG_IB_REQUEST: {
                cmd = duk_debug_read_int(thr);
                switch (cmd) {
                case DUK_DBG_CMD_BASICINFO: {
                        duk__debug_handle_basic_info(thr, heap);
                        break;
                }
                case DUK_DBG_CMD_TRIGGERSTATUS: {
                        duk__debug_handle_trigger_status(thr, heap);
                        break;
                }
                case DUK_DBG_CMD_PAUSE: {
                        duk__debug_handle_pause(thr, heap);
                        break;
                }
                case DUK_DBG_CMD_RESUME: {
                        duk__debug_handle_resume(thr, heap);
                        break;
                }
                case DUK_DBG_CMD_STEPINTO:
                case DUK_DBG_CMD_STEPOVER:
                case DUK_DBG_CMD_STEPOUT: {
                        duk__debug_handle_step(thr, heap, cmd);
                        break;
                }
                case DUK_DBG_CMD_LISTBREAK: {
                        duk__debug_handle_list_break(thr, heap);
                        break;
                }
                case DUK_DBG_CMD_ADDBREAK: {
                        duk__debug_handle_add_break(thr, heap);
                        break;
                }
                case DUK_DBG_CMD_DELBREAK: {
                        duk__debug_handle_del_break(thr, heap);
                        break;
                }
                case DUK_DBG_CMD_GETVAR: {
                        duk__debug_handle_get_var(thr, heap);
                        break;
                }
                case DUK_DBG_CMD_PUTVAR: {
                        duk__debug_handle_put_var(thr, heap);
                        break;
                }
                case DUK_DBG_CMD_GETCALLSTACK: {
                        duk__debug_handle_get_call_stack(thr, heap);
                        break;
                }
                case DUK_DBG_CMD_GETLOCALS: {
                        duk__debug_handle_get_locals(thr, heap);
                        break;
                }
                case DUK_DBG_CMD_EVAL: {
                        duk__debug_handle_eval(thr, heap);
                        break;
                }
                case DUK_DBG_CMD_DETACH: {
                        /* The actual detached_cb call is postponed to message loop so
                         * we don't need any special precautions here (just skip to EOM
                         * on the already closed connection).
                         */
                        duk__debug_handle_detach(thr, heap);
                        break;
                }
#if defined(DUK_USE_DEBUGGER_DUMPHEAP)
                case DUK_DBG_CMD_DUMPHEAP: {
                        duk__debug_handle_dump_heap(thr, heap);
                        break;
                }
#endif  /* DUK_USE_DEBUGGER_DUMPHEAP */
                case DUK_DBG_CMD_GETBYTECODE: {
                        duk__debug_handle_get_bytecode(thr, heap);
                        break;
                }
                case DUK_DBG_CMD_APPREQUEST: {
                        duk__debug_handle_apprequest(thr, heap);
                        break;
                }
#if defined(DUK_USE_DEBUGGER_INSPECT)
                case DUK_DBG_CMD_GETHEAPOBJINFO: {
                        duk__debug_handle_get_heap_obj_info(thr, heap);
                        break;
                }
                case DUK_DBG_CMD_GETOBJPROPDESC: {
                        duk__debug_handle_get_obj_prop_desc(thr, heap);
                        break;
                }
                case DUK_DBG_CMD_GETOBJPROPDESCRANGE: {
                        duk__debug_handle_get_obj_prop_desc_range(thr, heap);
                        break;
                }
#endif  /* DUK_USE_DEBUGGER_INSPECT */
                default: {
                        DUK_D(DUK_DPRINT("debug command unsupported: %d", (int) cmd));
                        duk_debug_write_error_eom(thr, DUK_DBG_ERR_UNSUPPORTED, "unsupported command");
                }
                }  /* switch cmd */
                break;
        }
        case DUK_DBG_IB_REPLY: {
                DUK_D(DUK_DPRINT("debug reply, skipping"));
                break;
        }
        case DUK_DBG_IB_ERROR: {
                DUK_D(DUK_DPRINT("debug error, skipping"));
                break;
        }
        case DUK_DBG_IB_NOTIFY: {
                DUK_D(DUK_DPRINT("debug notify, skipping"));
                break;
        }
        default: {
                DUK_D(DUK_DPRINT("invalid initial byte, drop connection: %d", (int) x));
                goto fail;
        }
        }  /* switch initial byte */

        DUK_ASSERT(duk_get_top(ctx) >= entry_top);
        duk_set_top(ctx, entry_top);
        duk__debug_skip_to_eom(thr);
        return;

 fail:
        DUK_ASSERT(duk_get_top(ctx) >= entry_top);
        duk_set_top(ctx, entry_top);
        DUK__SET_CONN_BROKEN(thr, 1);
        return;
}

DUK_LOCAL void duk__check_resend_status(duk_hthread *thr) {
        if (thr->heap->dbg_read_cb != NULL && thr->heap->dbg_state_dirty) {
                duk_debug_send_status(thr);
                thr->heap->dbg_state_dirty = 0;
        }
}

DUK_INTERNAL duk_bool_t duk_debug_process_messages(duk_hthread *thr, duk_bool_t no_block) {
        duk_context *ctx = (duk_context *) thr;
#if defined(DUK_USE_ASSERTIONS)
        duk_idx_t entry_top;
#endif
        duk_bool_t retval = 0;

        DUK_ASSERT(thr != NULL);
        DUK_UNREF(ctx);
        DUK_ASSERT(thr->heap != NULL);
#if defined(DUK_USE_ASSERTIONS)
        entry_top = duk_get_top(ctx);
#endif

        DUK_D(DUK_DPRINT("process debug messages: read_cb=%s, no_block=%ld, detaching=%ld, processing=%ld",
                         thr->heap->dbg_read_cb ? "not NULL" : "NULL", (long) no_block,
                         (long) thr->heap->dbg_detaching, (long) thr->heap->dbg_processing));
        DUK_DD(DUK_DDPRINT("top at entry: %ld", (long) duk_get_top(ctx)));

        /* thr->heap->dbg_detaching may be != 0 if a debugger write outside
         * the message loop caused a transport error and detach1() to run.
         */
        DUK_ASSERT(thr->heap->dbg_detaching == 0 || thr->heap->dbg_detaching == 1);
        DUK_ASSERT(thr->heap->dbg_processing == 0);
        thr->heap->dbg_processing = 1;

        /* Ensure dirty state causes a Status even if never process any
         * messages.  This is expected by the bytecode executor when in
         * the running state.
         */
        duk__check_resend_status(thr);

        for (;;) {
                /* Process messages until we're no longer paused or we peek
                 * and see there's nothing to read right now.
                 */
                DUK_DD(DUK_DDPRINT("top at loop top: %ld", (long) duk_get_top(ctx)));
                DUK_ASSERT(thr->heap->dbg_processing == 1);

                while (thr->heap->dbg_read_cb == NULL && thr->heap->dbg_detaching) {
                        /* Detach is pending; can be triggered from outside the
                         * debugger loop (e.g. Status notify write error) or by
                         * previous message handling.  Call detached callback
                         * here, in a controlled state, to ensure a possible
                         * reattach inside the detached_cb is handled correctly.
                         *
                         * Recheck for detach in a while loop: an immediate
                         * reattach involves a call to duk_debugger_attach()
                         * which writes a debugger handshake line immediately
                         * inside the API call.  If the transport write fails
                         * for that handshake, we can immediately end up in a
                         * "transport broken, detaching" case several times here.
                         * Loop back until we're either cleanly attached or
                         * fully detached.
                         *
                         * NOTE: Reset dbg_processing = 1 forcibly, in case we
                         * re-attached; duk_debugger_attach() sets dbg_processing
                         * to 0 at the moment.
                         */

                        DUK_D(DUK_DPRINT("detach pending (dbg_read_cb == NULL, dbg_detaching != 0), call detach2"));

                        duk__debug_do_detach2(thr->heap);
                        thr->heap->dbg_processing = 1;  /* may be set to 0 by duk_debugger_attach() inside callback */

                        DUK_D(DUK_DPRINT("after detach2 (and possible reattach): dbg_read_cb=%s, dbg_detaching=%ld",
                                         thr->heap->dbg_read_cb ? "not NULL" : "NULL", (long) thr->heap->dbg_detaching));
                }
                DUK_ASSERT(thr->heap->dbg_detaching == 0);  /* true even with reattach */
                DUK_ASSERT(thr->heap->dbg_processing == 1);  /* even after a detach and possible reattach */

                if (thr->heap->dbg_read_cb == NULL) {
                        DUK_D(DUK_DPRINT("debug connection broken (and not detaching), stop processing messages"));
                        break;
                }

                if (!thr->heap->dbg_paused || no_block) {
                        if (!duk_debug_read_peek(thr)) {
                                /* Note: peek cannot currently trigger a detach
                                 * so the dbg_detaching == 0 assert outside the
                                 * loop is correct.
                                 */
                                DUK_D(DUK_DPRINT("processing debug message, peek indicated no data, stop processing messages"));
                                break;
                        }
                        DUK_D(DUK_DPRINT("processing debug message, peek indicated there is data, handle it"));
                } else {
                        DUK_D(DUK_DPRINT("paused, process debug message, blocking if necessary"));
                }

                duk__check_resend_status(thr);
                duk__debug_process_message(thr);
                duk__check_resend_status(thr);

                retval = 1;  /* processed one or more messages */
        }

        DUK_ASSERT(thr->heap->dbg_detaching == 0);
        DUK_ASSERT(thr->heap->dbg_processing == 1);
        thr->heap->dbg_processing = 0;

        /* As an initial implementation, read flush after exiting the message
         * loop.  If transport is broken, this is a no-op (with debug logs).
         */
        duk_debug_read_flush(thr);  /* this cannot initiate a detach */
        DUK_ASSERT(thr->heap->dbg_detaching == 0);

        DUK_DD(DUK_DDPRINT("top at exit: %ld", (long) duk_get_top(ctx)));

#if defined(DUK_USE_ASSERTIONS)
        /* Easy to get wrong, so assert for it. */
        DUK_ASSERT(entry_top == duk_get_top(ctx));
#endif

        return retval;
}

/*
 *  Halt execution helper
 */

/* Halt execution and enter a debugger message loop until execution is resumed
 * by the client.  PC for the current activation may be temporarily decremented
 * so that the "current" instruction will be shown by the client.  This helper
 * is callable from anywhere, also outside bytecode executor.
 */

DUK_INTERNAL void duk_debug_halt_execution(duk_hthread *thr, duk_bool_t use_prev_pc) {
        duk_activation *act;
        duk_hcompiledfunction *fun;
        duk_instr_t *old_pc = NULL;

        DUK_ASSERT(thr != NULL);
        DUK_ASSERT(thr->heap != NULL);
        DUK_ASSERT(DUK_HEAP_IS_DEBUGGER_ATTACHED(thr->heap));
        DUK_ASSERT(thr->heap->dbg_processing == 0);

        DUK_HEAP_SET_PAUSED(thr->heap);

        act = duk_hthread_get_current_activation(thr);

        /* NOTE: act may be NULL if an error is thrown outside of any activation,
         * which may happen in the case of, e.g. syntax errors.
         */

        /* Decrement PC if that was requested, this requires a PC sync. */
        if (act != NULL) {
                duk_hthread_sync_currpc(thr);
                old_pc = act->curr_pc;
                fun = (duk_hcompiledfunction *) DUK_ACT_GET_FUNC(act);

                /* Short circuit if is safe: if act->curr_pc != NULL, 'fun' is
                 * guaranteed to be a non-NULL Ecmascript function.
                 */
                DUK_ASSERT(act->curr_pc == NULL ||
                           (fun != NULL && DUK_HOBJECT_IS_COMPILEDFUNCTION((duk_hobject *) fun)));
                if (use_prev_pc &&
                    act->curr_pc != NULL &&
                    act->curr_pc > DUK_HCOMPILEDFUNCTION_GET_CODE_BASE(thr->heap, fun)) {
                        act->curr_pc--;
                }
        }

        /* Process debug messages until we are no longer paused. */

        /* NOTE: This is a bit fragile.  It's important to ensure that
         * duk_debug_process_messages() never throws an error or
         * act->curr_pc will never be reset.
         */

        thr->heap->dbg_state_dirty = 1;
        while (thr->heap->dbg_paused) {
                DUK_ASSERT(DUK_HEAP_IS_DEBUGGER_ATTACHED(thr->heap));
                DUK_ASSERT(thr->heap->dbg_processing);
                duk_debug_process_messages(thr, 0 /*no_block*/);
        }

        /* XXX: Decrementing and restoring act->curr_pc works now, but if the
         * debugger message loop gains the ability to adjust the current PC
         * (e.g. a forced jump) restoring the PC here will break.  Another
         * approach would be to use a state flag for the "decrement 1 from
         * topmost activation's PC" and take it into account whenever dealing
         * with PC values.
         */
        if (act != NULL) {
                act->curr_pc = old_pc;  /* restore PC */
        }
}

/*
 *  Breakpoint management
 */

DUK_INTERNAL duk_small_int_t duk_debug_add_breakpoint(duk_hthread *thr, duk_hstring *filename, duk_uint32_t line) {
        duk_heap *heap;
        duk_breakpoint *b;

        /* Caller must trigger recomputation of active breakpoint list.  To
         * ensure stale values are not used if that doesn't happen, clear the
         * active breakpoint list here.
         */

        DUK_ASSERT(thr != NULL);
        DUK_ASSERT(filename != NULL);
        heap = thr->heap;
        DUK_ASSERT(heap != NULL);

        if (heap->dbg_breakpoint_count >= DUK_HEAP_MAX_BREAKPOINTS) {
                DUK_D(DUK_DPRINT("failed to add breakpoint for %O:%ld, all breakpoint slots used",
                                 (duk_heaphdr *) filename, (long) line));
                return -1;
        }
        heap->dbg_breakpoints_active[0] = (duk_breakpoint *) NULL;
        b = heap->dbg_breakpoints + (heap->dbg_breakpoint_count++);
        b->filename = filename;
        b->line = line;
        DUK_HSTRING_INCREF(thr, filename);

        return heap->dbg_breakpoint_count - 1;  /* index */
}

DUK_INTERNAL duk_bool_t duk_debug_remove_breakpoint(duk_hthread *thr, duk_small_uint_t breakpoint_index) {
        duk_heap *heap;
        duk_hstring *h;
        duk_breakpoint *b;
        duk_size_t move_size;

        /* Caller must trigger recomputation of active breakpoint list.  To
         * ensure stale values are not used if that doesn't happen, clear the
         * active breakpoint list here.
         */

        DUK_ASSERT(thr != NULL);
        heap = thr->heap;
        DUK_ASSERT(heap != NULL);
        DUK_ASSERT(DUK_HEAP_IS_DEBUGGER_ATTACHED(thr->heap));
        DUK_ASSERT_DISABLE(breakpoint_index >= 0);  /* unsigned */

        if (breakpoint_index >= heap->dbg_breakpoint_count) {
                DUK_D(DUK_DPRINT("invalid breakpoint index: %ld", (long) breakpoint_index));
                return 0;
        }
        b = heap->dbg_breakpoints + breakpoint_index;

        h = b->filename;
        DUK_ASSERT(h != NULL);

        move_size = sizeof(duk_breakpoint) * (heap->dbg_breakpoint_count - breakpoint_index - 1);
        if (move_size > 0) {
                DUK_MEMMOVE((void *) b,
                            (const void *) (b + 1),
                            (size_t) move_size);
        }
        heap->dbg_breakpoint_count--;
        heap->dbg_breakpoints_active[0] = (duk_breakpoint *) NULL;

        DUK_HSTRING_DECREF(thr, h);  /* side effects */
        DUK_UNREF(h);  /* w/o refcounting */

        /* Breakpoint entries above the used area are left as garbage. */

        return 1;
}

#undef DUK__SET_CONN_BROKEN

#else  /* DUK_USE_DEBUGGER_SUPPORT */

/* No debugger support. */

#endif  /* DUK_USE_DEBUGGER_SUPPORT */